The millivolt‑ampere reactive hour (mVAR·h) is the standard unit for measuring reactive energy—the cumulative amount of reactive power (measured in millivolt‑amperes reactive, mVAR) consumed or supplied over time. Represented by the symbol mVAR·h (or mVArh), this unit quantifies the non‑working power that oscillates between source and load in AC systems, influencing power factor and overall system efficiency. Engineers and utilities use mVAR·h to monitor and bill for reactive energy, optimize capacitor bank sizing, and assess the health of transformers and inductive loads. Its importance spans practical applications such as industrial energy management and scientific contexts like power quality analysis, making it a key metric for ensuring reliable, cost‑effective electrical operation.