Glossary
Data-center vocabulary — what the terms actually mean
The jargon developers use in hearings and filings, translated
into plain English. Every term links, so you can share
/glossary#pue in a comment thread.
| Term | Definition |
|---|---|
| PUE | Power Usage Effectiveness — ratio of total facility energy to IT energy. Lower is better; hyperscalers target 1.10–1.20. |
| WUE | Water Usage Effectiveness — liters of water per kWh of IT energy. Google fleet ~1.1 L/kWh; Meta claims 0.19. |
| CFE | Carbon-Free Energy — electricity from zero-carbon sources (solar, wind, nuclear, hydro). Distinct from RECs. |
| Hyperscaler | The largest cloud/AI companies that build their own data centers at massive scale (Google, Microsoft, Amazon, Meta). |
| Colocation (colo) | A data-center operator that leases space, power, and cooling to tenants — Equinix, Digital Realty, QTS, etc. |
| Interconnection queue | The list of projects waiting for grid connection approval from the regional operator (PJM, ERCOT, MISO, etc.). |
| Moratorium | A temporary ban or pause on new data-center construction, usually enacted by local or state government. |
| PPA | Power Purchase Agreement — a long-term contract to buy electricity from a specific generator, often renewable. |
| Rack density | The amount of power drawn per server rack, measured in kW. AI racks are 40–120+ kW vs. 5–15 kW traditional. |
| GPU | Graphics Processing Unit — specialized chips (NVIDIA H100, B200) that power AI training and inference. |
| Inference | Running a trained AI model to generate responses — what happens when you use ChatGPT, Gemini, etc. |
| Training | The initial process of building an AI model by processing massive datasets. Extremely energy-intensive. |
| Evaporative cooling | Cooling method that evaporates water to remove heat. Effective but water-intensive. |
| Liquid cooling | Piping coolant directly to server chips. More efficient for high-density AI workloads. |
| Marginal emissions | The CO₂ rate of the next power plant that would turn on to serve new load. The right signal for load-shifting. |
| Average emissions | The fuel-mix intensity of the whole grid. Answers a different question from marginal — used for inventory accounting. |
| Location-based carbon | Carbon accounting using the actual grid mix where energy is consumed. What a data center's real footprint looks like. |
| Market-based carbon | Carbon accounting after applying PPAs and certificates. Can be a fraction of location-based intensity. |
| Large-load tariff | A utility rate structure requiring very large customers to pay their own grid-upgrade costs, not socialize them onto ratepayers. |
| Capacity market | A market where utilities pay generators to be available on future peak days. Data-center demand is driving prices to record highs in PJM. |
| CBA | Community Benefits Agreement — a binding contract between a community and a developer setting terms like water caps, noise limits, and community payments. |
| Data dividend | A community fund into which per-MW annual payments are placed, distributed or reinvested locally — modelled on Alaska's oil dividend. |
| Clawback | A contractual provision allowing tax abatements or incentives to be recovered if the developer fails to meet promised commitments. |
| Decommissioning bond | A financial guarantee posted by the developer to cover site cleanup if the facility ceases operations. |
| Proffer | In Virginia land-use practice, a voluntary condition offered by a developer as part of a rezoning application. Should be recorded as binding. |
| Shell LLC | A limited-liability company (often with a fanciful name) used by hyperscalers to acquire land and file permits without revealing the parent. |
| Certificate of Public Convenience and Necessity (CPCN) | A regulatory approval a utility or generator must obtain before building. Some states exempt data-center backup power. |
| Substation | The facility that steps voltage down (typically from 115–765 kV transmission to 12–34 kV distribution) at the edge of a data-center campus. |
| RTO / ISO | Regional Transmission Organization / Independent System Operator — the operators that run the wholesale grid (PJM, ERCOT, MISO, SPP, CAISO, NYISO, ISO-NE). |
| FERC | The Federal Energy Regulatory Commission — regulates interstate wholesale electricity and transmission. ERCOT is the notable exception (Texas-only). |
| EIA-930 | The U.S. Energy Information Administration's real-time grid demand and generation dataset. What the calculator's Live Grid mode uses. |
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