Glossary
31 terms used across the Joule Ledger and our guides, defined in plain language.
Terms
- Autonomy
- The share of a mission a system can complete without new intake. Related: Reserve, Energy Return
- Bit erasure
- A logically irreversible operation that discards one bit of information. Related: Landauer limit, Landauer Gap
- Closure residual
- The share of intake not explained by the sum of the other accounts: (Intake − sum of accounts) / Intake. Related: Closure rule, Coverage factor
- Closure rule
- Intake = ΔReserve + Work + Overhead + Waste over the period. See the rule. Related: Closure residual, Coverage factor
- Coverage factor
- The multiplier applied to a standard uncertainty to give an expanded uncertainty; JL-26 uses k = 2. Related: Closure residual, Replicated
- Declared
- An audit grade: reported by the organization using JL-26. Related: Witnessed, Replicated
- Decision Yield
- Quality-passing decisions per unit of energy at a stated meter point. See Decision Yield. Related: Quality gate, Useful decision
- Energy Return
- Energy delivered over the lifetime energy invested. See Energy Return. Related: EROI, Autonomy
- EROI
- Energy return on investment: the energy a source delivers divided by the energy invested to obtain it. Related: Energy Return, Intake
- Estimated
- A result label: key values metered, the rest calculated or simulated with stated assumptions. Related: Measured, IPMVP
- Intake
- All energy entering the system, from any source. Related: Reserve, Closure rule
- IPMVP
- The International Performance Measurement and Verification Protocol, whose options A to D describe ways of verifying energy savings. Related: Measured, Estimated
- Landauer Gap
- Energy per irreversible bit operation divided by the Landauer limit. See the Landauer Gap. Related: Landauer limit, Bit erasure
- Landauer limit
- The minimum energy to erase one bit, kB·T·ln 2: about 2.87 × 10−21 J at 300 K. Related: Landauer Gap, Bit erasure
- Measured
- A result label: all accounts metered at the stated meter point. Related: Estimated, Projected
- Meter point
- The physical boundary where energy is measured, M1 to M4. See meter points. Related: MLPerf Power, Overhead Ratio
- MLPerf Power
- The MLCommons method for measuring the energy of benchmark runs, at a system boundary that excludes cooling. Related: Meter point, Decision Yield
- Overhead
- Energy that keeps the system able to work: cooling, life support, idle draw, power conversion. Related: Overhead Ratio, Waste
- Overhead Ratio
- Energy at the outer boundary over energy at the inner boundary; for a data center, M4 over M3, it equals PUE. See Overhead Ratio. Related: PUE, Partial PUE
- Partial PUE
- A PUE-style ratio that covers only part of a facility; JL-26 requires it to be labeled partial. Related: PUE, Overhead Ratio
- Projected
- A result label for a forward-looking figure. Related: Measured, Estimated
- PUE
- Power usage effectiveness: total facility energy divided by IT equipment energy, defined in ISO/IEC 30134-2. Related: Overhead Ratio, WUE
- Quality gate
- The stated standard a task must meet to count as a useful decision. Related: Useful decision, Decision Yield
- Rating scheme
- The EU scheme grading data centers A to G for energy and water. See the guide. Related: PUE, WUE
- Replicated
- An audit grade: reproduced independently within the combined uncertainty. Related: Witnessed, Coverage factor
- Reserve
- Energy held in storage; the ledger records its change over the period. Related: Intake, Autonomy
- Useful decision
- A completed task from the versioned task set that passes its stated quality gate. Related: Quality gate, Work
- Waste
- Energy that left as heat without doing work or overhead. Related: Overhead, Closure residual
- Witnessed
- An audit grade: measured with AAERL present. Related: Declared, Replicated
- Work
- Energy that produced completed useful decisions or tasks. Related: Useful decision, Overhead
- WUE
- Water usage effectiveness: a facility's water use relative to its IT energy, used for the EU water grade. Related: PUE, Rating scheme
Keep reading
JL-26 overviewJL-26, the Joule Ledger: five energy accounts that must close, four meter points, five ratios, and labels and grades for every result.The five ratiosThe five JL-26 ratios: Decision Yield, Overhead Ratio, Landauer Gap, Energy Return and Autonomy, with their formulas, units and which direction is better.The EU rating schemeThe EU data-center rating scheme adopted 21 September 2026: separate A-to-G grades for energy (PUE) and water (WUE), who it covers, and the 2027 dates.All guidesPlain, sourced guides to measuring AI and data-center energy: the EU rating scheme, EU reporting, inference energy, benchmarks and how metrics get gamed.
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Plain definitions of AI and data-center energy measurement terms, from PUE, WUE and meter points to the Landauer limit, Decision Yield and audit grades.