The Data Center Glossary: What the AI headlines have been saying all along
Every megawatt, lease, and waiting list in the news, translated into words a reader already holds. Fifty-six terms from the building, the power grid, and the money behind them.
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TL;DR
The AI buildout is described in three separate professional vocabularies, and almost no article tells the reader which one it is using. Data center coverage borrows from commercial real estate, from electrical engineering, and from project finance. A reader fluent in one of the three is still lost in the other two.
The terms that cause the most confusion are the ones that sound ordinary. Words including load, tier, capacity, stranded, and platform each carry two or three unrelated meanings inside the same sector, and headlines move between those meanings without warning.
The vocabulary decides public outcomes, not only private ones. Whether a data center gets built, how long it waits for electricity, who pays for the power lines it needs, and whether a town approves it are all settled in these words, in filings and hearings that are open to the public.
A sentence like this one appears in data center coverage most weeks:
“The developer secured 300 MW behind the meter, signed a fifteen-year triple-net lease with a hyperscaler, and is still sitting in the interconnection queue.”
Nine words in that sentence are doing real work, and a reader who has followed the AI story closely for two years may still be unable to define a single one of them.
The sector never wrote anyone a glossary. This vocabulary was built by people who assumed that everybody in the room already had it.
The reason the vocabulary is so hard is worth stating plainly, because it explains why other explainers have not fixed it.
Data centers sit at the intersection of three industries that were unrelated until recently.
Commercial real estate contributed the language of leases, tenants, and yields.
Electrical engineering contributed megawatts, substations, and redundancy. Project finance contributed the debt structures that pay for all of it.
Each of those fields had a century to build its own jargon. Then they collided in a single building, and nobody harmonized the dictionaries.
What follows is that dictionary. It is organized the way the sector actually divides: the building, the power, and the money.
Each term gets a plain definition, what it decides in practice, and where a reader is likely to meet it.
At the end are five ordinary-looking words that carry more than one meaning, which are the words that cause the most trouble.
The building
Start here, because the physical object is the one thing in this sector a reader can picture without help.
A data center is a warehouse full of computers. The computers are servers, which are desktop computers with the screen and keyboard removed and the working parts flattened into a tray.
The trays slide into a rack, which is a tall metal shelf about the height of a refrigerator, holding dozens of them. A large building holds thousands of racks.
Everything else in this section describes how those racks are housed, cooled, powered, and sold.
Hyperscale and hyperscaler. A hyperscaler is one of the handful of companies that operate computing at planetary scale and build data centers for their own use: Amazon, Microsoft, Google, and Meta are the names a reader already knows.
Hyperscale describes a facility built to their standard, which generally means a campus rather than a single building.
The word appears in almost every article about the buildout, and it is a description of the customer as much as the structure.
Colocation. A business that owns the building and rents space, power, and cooling to companies that own the computers.
The tenant brings its own servers and pays for the room and the electricity to run them.
Retail colocation rents by the rack or the cage to smaller customers.
Wholesale colocation rents in blocks of megawatts to large ones. A reader will see the word shortened to colo.
Rack. The metal frame that holds servers. Capacity is measured by the electricity a rack can draw, which is why data centers are sized in megawatts rather than square feet.
Density, power density, rack density. How much electricity a single rack consumes.
This is the number that changed when AI arrived. A rack of ordinary business servers draws a modest amount and can be cooled with moving air.
A rack built for AI training packs far more computing into the same shelf and produces heat that air cannot carry away fast enough.
NVIDIA’s GB200 NVL72, which holds 72 of its Blackwell chips in one rack, is described by NVIDIA itself as a liquid-cooled design for exactly this reason.
Density is why the buildings had to be redesigned rather than simply multiplied.
Liquid cooling. Running coolant through pipes directly to the hot components of the server instead of blowing cold air at them.
Direct-to-chip cooling brings the liquid to a plate mounted on the processor.
Immersion cooling submerges the whole server in a fluid that does not conduct electricity.
Both exist because high-density racks generate more heat per square foot than air can remove, and both add plumbing to buildings that previously needed only fans.
Latency. The delay between a request and a response, measured in thousandths of a second. Distance creates latency, because signals take time to travel.
This is why a video call routes through a nearby facility while a large AI model can be trained in a remote one: the training run does not care about the delay, and the video call does.
Training and inference. Training is the one-time process of building an AI model (ChatGPT, Gemini, Claude, etc) by running enormous amounts of data through it, which takes months and vast amounts of electricity in one place.
Inference is what happens every time someone asks the finished model a question, which takes a fraction of a second and happens billions of times.
Training built the industry’s early demand.
Inference is the demand that keeps growing after the model is finished.
Redundancy, N+1, 2N. Spare equipment held ready so that a failure does not stop the building. N is the amount of equipment needed to run at full load.
N+1 means one spare unit beyond that.
2N means a complete duplicate of everything. Redundancy is most of what separates a data center from a warehouse, and most of what it costs.
Tier III and Tier IV. A certification system run by the Uptime Institute, an independent body, that rates how much of a building can be repaired or replaced while it keeps running.
Tier III means maintenance can happen without shutting anything down.
Tier IV adds tolerance for an unplanned equipment failure on top of that.
Operators cite the ratings in marketing, and buyers of space treat them as a floor rather than a distinction.
PUE, or power usage effectiveness. A ratio comparing all the electricity a facility draws against the portion that reaches the computers.
A score of 1.0 would mean every unit of power went to computing and none to cooling or lighting. Real buildings score above that, and the gap is the overhead.
PUE is the industry’s headline efficiency number and the one most often quoted without explanation.
WUE, and water. Water usage effectiveness measures liters of water consumed per unit of computing.
It exists because one common way to cool a building cheaply is to evaporate water, which trades electricity for a local water supply.
This is the term at the center of most community objections to new sites, particularly in dry regions, and operators are now asked about it in public hearings.
Greenfield, brownfield, retrofit. Greenfield means building on empty land.
Brownfield means building on a site that was previously industrial, often chosen because it already has a heavy power connection.
Retrofit means rebuilding the inside of an existing data center, which is now common as older buildings designed for low-density racks are converted for AI.
Speculative build. Starting construction before any customer has signed for the space.
The developer is betting demand will arrive. In a slow market this is how companies fail.
In the current market it is how they win, because a building already under construction can be delivered years sooner than one that starts after the contract is signed.
Build-to-suit. The opposite arrangement, where a customer commits first and the developer builds to that customer’s specification.
Lower risk for the developer, and a longer wait for the tenant.
Most large campuses are one of these two things, and knowing which tells a reader how much risk somebody took.
Powered shell. A finished building with electricity brought to it and very little else inside.
The buyer installs its own cooling and electrical fit-out.
It is sold this way because the shell and the power are the slow parts to obtain, and the equipment inside can be added quickly by whoever will operate it.
Commissioning. The testing period after construction and before customers move in, when every system is deliberately failed to confirm the backups work.
It takes months and it is the last thing to be compressed when a schedule slips.
Transformer, switchgear, UPS, generator. The chain of equipment between the public power lines and the chips.
A transformer changes electricity from the high voltage used to move it long distances to the lower voltage a building can use.
Switchgear routes and isolates it. A UPS, or uninterruptible power supply, is a bank of batteries that carries the load for the seconds between a grid failure and the generators starting.
The generators, usually diesel, run the site until the grid returns.
Transformers in particular now have delivery waits measured in years, which has made a piece of electrical equipment into a scheduling constraint on the AI buildout.
Subsea cable, dark fiber, cross-connect, peering. How a building talks to the world.
Subsea cables are the fibre-optic lines on the ocean floor that carry almost all intercontinental internet traffic.
Dark fiber is cable already laid in the ground but not yet lit with equipment, which a buyer can lease and light itself.
A cross-connect is a physical cable joining two customers inside the same facility.
Peering is two networks agreeing to exchange traffic directly rather than paying a third party to carry it.
AI factory. A term promoted by chip makers and adopted by operators for a facility built for AI training rather than general computing.
It reflects a real design shift, mainly much higher density and widespread liquid cooling. But it is also a marketing term, so readers should treat it as a description of intent, not a technical standard.
If a reader takes one thing from this section, it is that the building is measured in electricity rather than in space.
Every argument in the next section follows from that, and missing it is why the phrase “a 500 MW data center” reads as a fact about size when it is a fact about consumption.
The power
This vocabulary comes from the electricity industry, which is regulated, slow-moving, and public. It is also where the AI story now actually happens.
Megawatt and gigawatt. A watt measures the rate at which electricity is used. A megawatt is a million watts and a gigawatt is a billion. Scale it with a household.
The US Energy Information Administration puts average annual consumption for a residential utility customer at 10,791 kilowatt-hours.
A facility drawing 100 megawatts continuously for a year consumes roughly what 80,000 American homes consume in that year.
When a company announces a gigawatt campus, it is describing something on the order of a mid-sized city’s electricity demand.
The grid. The network of power stations, high-voltage lines, and local wires that delivers electricity to everyone connected to it.
Its defining property is that supply and demand must match continuously, second by second, because electricity in bulk cannot be stored easily.
Every constraint in this section comes back to that property.
Interconnection, and the interconnection queue. Interconnection is the permission and the physical work required to connect a new power plant or a new large customer to the grid.
The queue is the waiting line for it, and it is long. The Lawrence Berkeley National Laboratory publishes the count in its Queued Up report.
The 2026 edition, released in June 2026 with data through the end of 2025, found over 2,060 gigawatts of generation and storage capacity actively waiting to connect.
It also found that for projects finished in 2025, the median wait from application to operation ran past five years.
Hold that against a construction schedule of roughly two years, and the shape of the whole sector becomes clear: the building is the fast part.
Utility, ratepayer, tariff, rate case. The utility is the company that delivers electricity in a given territory, usually a regulated monopoly.
Ratepayers are its customers, meaning households and businesses.
A tariff is the published schedule of what each class of customer pays. A rate case is the public proceeding where a utility asks its regulator to change those prices.
Data centers have made rate cases newsworthy, because the question of who pays for new power lines and new generation is settled in them, in public, with transcripts.
Transmission and substation. Transmission is the high-voltage long-distance network that moves bulk electricity between regions.
A substation is the facility where voltage is stepped from transmission levels down to something a customer can use.
A site with a substation nearby is worth substantially more than one without, which is why land near existing electrical infrastructure has been bought aggressively.
Energization and time-to-power. Energization is the moment a site is actually connected and can draw electricity.
Time-to-power is the industry’s phrase for how long that takes from the decision to build.
It has replaced construction cost as the number that decides where projects go, and it is why regions with spare grid capacity now attract investment that would once have followed cheap land.
Stranded power. Electricity that exists but cannot reach a customer, usually because the wires to carry it were never built or the plant sits far from demand.
Developers hunt for it, because a site next to stranded power can skip years of waiting.
This word does a second job elsewhere in finance, which is covered at the end.
Offtake and offtaker. An offtake agreement is a long-term contract in which a buyer commits in advance to purchase what a project produces. The offtaker is that buyer.
The term comes from mining and energy, and it matters because a signed offtake is usually what allows a project to raise money at all.
Lenders are financing the contract as much as the asset.
PPA, or power purchase agreement. A specific kind of offtake for electricity. A buyer agrees to purchase power from a particular plant, at an agreed price, for ten or twenty years.
The technology companies use these to fund new wind, solar, and nuclear capacity, because a signed twenty-year buyer is what makes a plant financeable.
Baseload and firm power. Baseload is electricity available continuously rather than when the weather permits.
Firm power is a contractual promise that a specified amount will be there when called for.
Data centers need both, because a training run interrupted at hour 600 is a very expensive failure.
This requirement is why nuclear generation returned to the conversation after two decades of decline.
Behind-the-meter. A power arrangement where generation sits on the customer’s side of the utility’s meter, so the electricity never travels on the public grid.
In front of the meter means the ordinary arrangement where power is bought from the grid. Behind-the-meter is attractive because it can bypass the interconnection queue.
It is contentious because a large customer generating its own power may contribute less to the shared cost of the network that everyone else still relies on, and regulators are actively arguing about it.
On-site generation, gas turbines, fuel cells. Power produced at the site itself. A gas turbine is essentially a truck-sized jet engine burning natural gas to spin a generator.
A fuel cell converts fuel to electricity chemically, without combustion.
Both are being installed at data centers as bridge power, meaning a temporary supply while the grid connection is waited out, and both attract local objection over air quality.
Nuclear, and SMR. Nuclear plants supply large amounts of continuous, carbon-free electricity, which matches what a data center needs almost exactly.
SMR stands for small modular reactor, a smaller design intended to be factory-built and delivered rather than constructed on site.
Several are under development and none is yet delivering power at commercial scale in the United States, so announcements in this area describe intentions on a timescale of the 2030s.
Curtailment. Deliberately reducing output or consumption because the grid cannot handle it at that moment.
Wind farms are curtailed when they generate more than the wires can carry.
Data centers are now being asked to accept curtailment of their own demand in exchange for faster connection, which turns a computing facility into a flexible participant in the grid rather than a fixed drain on it.
Battery storage and microgrids. Battery storage holds electricity for minutes or hours, smoothing the gap between when power is generated and when it is needed.
A microgrid is a local system that can disconnect from the main grid and run independently.
Both appear in data center plans as ways to reduce dependence on a connection that may not arrive on schedule.
Carbon-free energy and RECs. A renewable energy certificate is a tradeable document representing one unit of electricity generated from a renewable source.
Because electrons cannot be traced through wires, certificates are how a company claims renewable power.
Buying certificates from a distant wind farm and matching them against consumption in a different region is called annual matching.
Matching consumption to carbon-free generation in the same place and the same hour is called 24/7 carbon-free energy, and it is a much harder claim to make.
Load growth. The rate at which total electricity demand rises. It was close to flat in the United States for roughly two decades, which shaped how utilities planned, hired, and ordered equipment.
It is now rising again, and much of the current strain follows from an industry that spent twenty years optimizing for a world that stopped existing.
ERCOT, PJM, and what an RTO is. A regional transmission organization operates the grid across a multi-state area and runs the market that sets wholesale electricity prices there.
PJM covers thirteen states across the mid-Atlantic and Midwest.
ERCOT covers most of Texas and is notable for being largely separate from the rest of the country’s grid.
A reader meets these names constantly in data center coverage because the region determines both the wait and the price.
Moratorium. A pause or ban on new data center connections or approvals, imposed by a local government or a utility. Several jurisdictions in the United States and in Europe have adopted one.
Moratoriums are the clearest evidence that the constraint on this buildout is no longer capital or chips, and the reasons cited are usually electricity prices, water, and land use.
The thing to carry out of this section is that the electricity system was built to serve demand that grew slowly and predictably, and it is being asked to serve demand that does neither.
When you see a story about an AI project delayed, the delay is far more often a power problem than a construction or funding problem.
The money
This vocabulary comes from commercial real estate and project finance. It is essential for understanding why buildings get built and appears throughout industry earnings reports and press releases.
Capex and opex. Capital expenditure is money spent to build or buy something lasting. Operating expenditure is money spent running it.
The enormous figures announced by technology companies for data centers are capex, which is why they appear as investment commitments rather than as costs against current profit.
Lease, tenant, anchor tenant. A data center operator is a landlord, and the arrangement works much like renting an apartment, with a contract, a term of years, and a monthly payment.
The tenant is the company renting. An anchor tenant is a large one whose commitment makes the rest of the building financeable, in the same way a department store anchors a shopping mall.
Triple net. A lease in which the tenant pays the taxes, the insurance, and the maintenance on top of the rent.
The landlord’s income is therefore closer to predictable, because most of the costs that could vary belong to somebody else.
Long triple-net leases with large technology companies are the reason data centers can be financed with debt on terms usually reserved for far duller assets.
Take-or-pay. A contract in which the customer pays whether or not it uses what it reserved.
The phrase is literal. Take-or-pay commitments underpin most large power and capacity deals in this sector, and they are what a lender is really lending against.
Backlog, contracted revenue, RPO. All three describe money a company has signed for but not yet earned.
RPO stands for remaining performance obligations, a formal accounting measure of contracted revenue not yet delivered.
These figures appear prominently in cloud company results, and they matter because they indicate demand that is committed rather than forecast.
Pre-leasing and lease-up. Pre-leasing is signing tenants before a building is finished.
Lease-up is the period after completion during which remaining space fills. A campus that is fully pre-leased before it opens tells a reader something about demand that no forecast can.
Vacancy and absorption. Vacancy is finished capacity with nobody in it. Absorption is the rate at which new capacity gets taken up. In most property markets these move independently.
In this one, vacancy in the major markets has been unusually low, which is why so much construction begins without a signed customer.
Capital stack. The layered set of money funding a project, ordered by who gets repaid first.
Senior debt sits at the bottom and is repaid first at the lowest return. Equity sits at the top, is repaid last, and takes the loss if the project disappoints.
Every announcement about a project being financed is a statement about who occupies which layer.
Project finance and non-recourse. Project finance lends against a single asset’s own future income rather than against the borrower’s whole balance sheet.
Non-recourse means that if the project fails, the lender can take the project and nothing else.
This structure allows very large facilities to be built by companies that could not borrow those sums against themselves.
REIT. A real estate investment trust, a company that owns income-producing property and is required to distribute most of its earnings to shareholders in exchange for favorable tax treatment.
Equinix and Digital Realty are the two large listed data center REITs, and they are the reason a reader can find data center ownership inside an ordinary retirement fund.
Private credit. Lending by investment funds rather than by banks.
It has grown substantially since the 2008 financial crisis, and it is now a major source of data center construction funding, partly because these loans are larger and more bespoke than banks readily provide.
ABS, securitization, asset-backed. Securitization is the practice of bundling the future payments from a set of contracts into a bond that investors can buy.
ABS stands for asset-backed securities, the bonds themselves.
Data center leases have become a recognised category of collateral for this, which means the rent from a specific building is being converted into a tradeable instrument bought by pension funds and insurers.
Joint venture. Two or more parties forming a shared entity to develop something neither would fund alone.
Nearly every very large campus announced in the past two years has been structured this way, typically pairing a developer that knows how to build with an investor that supplies the money.
Cap rate. Short for capitalization rate. Annual income divided by the price paid, expressed as a percentage.
It is the standard shorthand for how expensive a property is relative to what it earns.
A lower cap rate means a higher price for the same income, and the number is quoted constantly in property coverage without ever being defined.
Stabilized, and stabilized yield. A building is stabilized once it is fully leased and running normally rather than filling up.
Stabilized yield is the annual income at that point divided by the total cost to build.
The gap between what a completed building yields and what an equivalent one costs to buy is where development profit comes from.
IRR. Internal rate of return, the annualized return on an investment, accounting for when the money went out and when it came back.
Timing is the point: the same total profit earned in three years produces a much higher IRR than in ten.
A reader will see it quoted alongside EBITDA, which measures operating earnings before interest, tax, and the accounting charges for wear and obsolescence.
The two answer different questions, and they are routinely presented as though they answered the same one.
Depreciation and useful life. Depreciation is the accounting practice of spreading the cost of equipment across the years it is expected to work. Useful life is the assumed number of those years.
This obscure pairing is now central to the AI boom debate: if chips wear out or become obsolete faster than assumed, industry profits may be overstated relative to the underlying economics.
Anyone following the debate about whether the buildout is overstated is following an argument about this number.
Circular deals. Arrangements in which a supplier invests in its own customer, or a company’s revenue is partly funded by its own investment.
Several such arrangements between chip makers, cloud providers, and AI developers have been announced and publicly disputed.
Supporters argue that suppliers funding a new market is ordinary practice in capital-intensive industries and has precedent in telecoms and semiconductors.
Critics argue the structure can make demand appear more independent than it is, and that the same practice preceded losses in earlier technology cycles.
The disagreement is genuine and unresolved, and a reader should know the term because it will keep appearing.
What this section shows is that the buildings get built because somebody signed a contract long enough to borrow against.
When you read that a project is “financed,” the real event is that a technology company promised to pay for fifteen years, and everything else followed from that promise.
Five words that do two jobs
These are the words that cause the most trouble, because none of them looks like jargon. A reader who has understood everything above can still be defeated by a headline built on one of these.
Load. To an electrical engineer, load is demand for electricity. To a computing person, load is the amount of work a machine is doing. When an article says load growth, it means the first.
When it says workload, it means the second. Both appear in the same paragraph regularly.
Tier. Three unrelated meanings. A Tier III building is a reliability rating from the Uptime Institute. A Tier 1 market is a mature metropolitan area with established data center supply, such as Northern Virginia.
A tier of the capital stack is a layer of financing. Nothing connects the three except the word.
Capacity. Grid capacity is how much electricity the wires can carry. IT capacity is how much computing a building can house.
Contracted capacity is how much a customer has already committed to pay for.
Three different numbers, all quoted in megawatts, all called capacity, and frequently compared to each other as though they measured the same thing.
Stranded. Stranded power is electricity that exists and cannot reach a buyer, which is an opportunity for whoever can get to it.
A stranded asset is an investment that loses its value before the end of its expected life, which is a loss.
The word points in opposite directions depending on which industry is speaking.
Platform. In investment language, a platform is the first company an investor buys and then builds around through further acquisitions. In technology, a platform is a service other people build on, such as a cloud.
In development, a platform is the physical campus itself. All three usages are common in the same coverage.
Very little of this vocabulary was written to be understood by the public.
It was written by three professions talking to themselves, and it stayed private because for most of its history nothing about it touched anyone outside the industry.
That has changed. The International Energy Agency estimated that data centers consumed about 415 terawatt-hours of electricity in 2024, or 1.5% of global demand, and projects that consumption will more than double to roughly 945 terawatt-hours by 2030.
Decisions of that size are made in rate cases, in zoning hearings, and in interconnection queues, and every one of those proceedings is conducted in the words above.
They are open to the public and they are effectively closed to anyone who cannot read them.
The AI that answers a question in a second sits on top of a building somebody had to power, a grid somebody had to expand, and a contract somebody had to sign for fifteen years. Now you can read the sentences that describe it.
Which of these words had you seen a dozen times without ever knowing what it meant?