For anyone reading their first data center quote. Where marketing bends a term, the entry says what it really means.

Terms#

Grouped by topic: space, power, connections, resilience, compliance and contracts. Every definition stands on its own.

Colocation#: Also called: data center space; Renting space, power and cooling in someone else's data center for servers you own and run. The building, power and cooling are theirs. The servers and software stay yours.; Different from cloud, where you rent the computers, and managed hosting, where someone else runs them. Most companies mix all three.
Cabinet#: Also called: rack, cab; The smallest standard unit of data center space: a lockable cabinet, usually 42 to 52 rack units tall, that you fill with your own gear. It's usually priced per cabinet per month, plus power.
Rack unit#: Also called: RU, U; How cabinet height is measured: one rack unit is 1.75 inches. A "2U" server takes two. It matters mostly when you rent part of a cabinet.
Cage#: A fenced-off area on a shared data center floor, holding several cabinets. You buy one when security or compliance means your gear must be separate. The fencing is priced on its own.
Suite#: Also called: private suite, data hall; A private room inside a data center, with its own walls and door. It's the step above a cage, and where deals start to be quoted like the big ones.
Retail colocation#: The providers' word for data center space sold by the cabinet, cage or suite, usually on 12 to 36-month terms. It's what most buyers under about a megawatt are shopping for.; Each provider draws its own line with the bigger deals, anywhere from about 1 MW to 10 MW. Near a megawatt? Ask for it quoted both ways.
Wholesale colocation#: The providers' word for whole halls or megawatt blocks, on long terms, usually five to fifteen years. It's priced per megawatt, and usually cheaper per kW because the provider does less.
Powered shell#: A building with power and structure but no data center fit-out, which you finish yourself. Cheapest and most work, for buyers who can build.
Build-to-suit#: Also called: BTS; A data center or hall built to one tenant's spec. It takes about six months to over two years, and it's negotiated like a development deal, not a normal order.
Raised floor#: The raised floor in a data hall that cooling air and cables once ran under. The number matters because it describes the real usable space. That can be a small slice of a building's total square footage.
Campus#: Several buildings run by one company on one site. It muddles counts: a provider may call a campus one location while others count each building. Two honest counts can differ a lot.
kW and MW#: Kilowatts and megawatts: how much power you use, and what data center space is priced on. Power describes your project better than cabinet count. Same cabinets at different power are different products.
Density#: Also called: kW per rack, kW per cabinet; How much power one cabinet draws. Ordinary business servers run a few kW per cabinet. AI and high-performance gear runs tens of kW and up. Density decides which buildings fit, whether you need liquid cooling, and what you pay.
Committed power#: Power you reserve and pay for whether you use it or not. The usual model for cabinets and cages. Reserving from equipment labels instead of measured draw is one of the most expensive mistakes buyers make.
Metered power#: Power billed on what you actually use. Often sold as a reserved base with metered billing above it. Ask which model a quote uses, because the same rate gives very different bills.
Breakered power#: Power sold as circuits of a set size, not by what you use. You can't safely run a circuit to its limit. You're buying the circuit, so you don't get money back for what you don't use.
N+1#: One spare beyond what the load needs, like four cooling units where three would do. It covers one part failing, not a whole power path.
2N#: Everything doubled: two full systems, each able to carry the whole load. Safer and pricier than N+1. Paying for 2N when N+1 would do is a common overspend.; You'll also see 2N+1 and 2N+2, meaning doubled plus extra spares.
PUE#: Also called: Power Usage Effectiveness; How efficient a building is: total energy divided by the energy reaching your servers. At 1.5, cooling and losses burn half again what your servers use. Lower is better.; It matters if your bill depends on it or efficiency is a must for you. A design target isn't a measured number, so compare like with like.
WUE#: Also called: Water Usage Effectiveness; Water used per unit of server energy. It matters more in dry cities, where water use draws regulators and headlines.
Liquid cooling#: Cooling with liquid instead of air, piped to the chip or with servers dunked in fluid. Modern AI hardware usually needs it. Ask about each building, not the provider as a whole.
Cross-connect#: Also called: XC; A cable, fiber or copper, from your gear to a carrier, a cloud or another tenant in the same building. Billed monthly per connection, plus an install fee.; The cost buyers miss most. In busy setups it can match what you pay for cabinets. You often pay at both ends, and removing one early can cost extra. Count them and price them over the full term.
Meet-me room#: Also called: MMR; The shared room in a data center where carriers and tenants plug into each other. How many networks meet there is much of what makes a building well connected.
Carrier hotel#: A building whose real value is the networks packed into it. Usually decades old and downtown. It can't be copied, because the fiber meets there and always has.
Carrier-neutral#: Also called: network-neutral; You can bring in any network provider you like, instead of buying from the owner. Nearly every data center is neutral now, so confirm which carriers are actually in your building.
On-net#: A carrier is on-net when its network already reaches the building, so one cable connects you. If it isn't, it has to build in, which costs money and months. Ask for your building's list.
Cloud on-ramp#: A private line into a cloud, like AWS Direct Connect or Azure ExpressRoute. It skips the public internet, so it's faster and steadier.; OFTEN STRETCHED. "On-ramp available" usually means reached over a network, not inside your building. Both work, but they differ in speed and in who you call when it breaks. Ask whether yours is in this building.
Internet exchange#: Also called: IX, IXP; A shared hub where many networks swap traffic directly, usually for free, instead of paying to route it. A major exchange in your building is a real edge if you move a lot of traffic.
Point of presence#: Also called: PoP; A spot where a network company keeps gear, often one rack in someone else's data center. A PoP isn't space you can rent.; It skews published counts. Directories that list by address count these as data centers, which can double a provider's apparent size. If you can't rent space there, it doesn't count.
Software-defined interconnection#: Also called: NaaS, virtual cross-connect; Connections ordered in a web portal instead of as a physical cable. Priced separately, usually by port and speed. Faster to set up, but it adds a step and another company.
Dark fiber#: Also called: dark fibre; Unlit fiber you lease between two places and light with your own gear. It links buildings on a campus, and reaches a carrier hotel from a cheaper building nearby.
Uptime Institute Tier#: Also called: Tier I, II, III, IV; The outside rating of how well a data center is built to stay up, awarded by the Uptime Institute per building. Higher tiers mean more backup. A certified building has a certificate and a number.; THE MOST MISUSED TERM HERE. "Tier III design", "Tier III standards", "equivalent" and "quality" are all self-declared. "Tier 5" isn't an Uptime tier at all. Real certification is rare, even at the biggest providers, so ask for the certificate number and the building it names.
Concurrently maintainable#: Any single part can be taken offline for maintenance without cutting your power. It matters most day to day, because planned maintenance happens far more often than failures.
SOC 2#: An outside auditor's report that a company's security controls work as described. A Type 2 report covers a stretch of time, not one day, and it's the one that counts.; Ask for the report and check what it covers. It's often limited to named buildings, sometimes ones the provider no longer owns. A logo on a website isn't an audit letter.
ISO 27001#: An international security certification. Like SOC 2, it covers specific things, so confirm it covers your building, not just the company.
PCI DSS#: The card payment industry's security standard. The building can cover the physical side, but that doesn't make your setup compliant. Confirm who covers what.
HIPAA and BAA#: The US health data privacy law. There's no such thing as a HIPAA certification. What matters is whether the provider will sign a Business Associate Agreement (BAA), so ask for the BAA.
FedRAMP and ATO#: The US government's security approval for cloud services, and the Authority to Operate issued under it, at Moderate or High levels.; Often misread. It may cover a provider's software, not its data centers. When it covers buildings, it's usually specific named ones. Ask what's approved, at what level, and for which building.
MRC and NRC#: Monthly recurring charge and non-recurring charge: the monthly rent and the one-time costs. One-time costs cover setup, cage or suite build-out, power and connection installs. Ask for them itemized.
Escalator#: The yearly price increase in your contract. Almost every deal has one, and nobody publishes it. It compounds and it's negotiable, so get the percentage in writing before you sign.
Evergreen auto-renewal#: A contract that renews itself unless you cancel inside a notice window. Nearly every rack and cage contract has it. Know the window, set a reminder, and cap the renewal price.
Remote hands#: Basic hands-on help from the data center's staff, like reboots and cable checks. Billed hourly with a minimum, and more after hours. Prepaid blocks usually cost less.
Smart hands#: Skilled on-site work like installs, setup and troubleshooting, priced above remote hands. Confirm where the provider draws the line, because it decides which rate you pay.
SLA and service credits#: The promised service level, and what the provider pays when it misses. The credit schedule is what matters. A big uptime promise with a tiny credit protects them, not you, so get the schedule and the claim process in writing.
Total contract value#: Also called: TCV; The full cost over the whole term, with yearly increases, one-time charges and connection fees in. It's the only number that fairly compares two offers, and the one providers rarely lead with.

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Data center glossary for buyers: colocation terms in plain English

Terms#

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