Definition: A watt-hour (symbol Wh) is a unit of energy equal to one watt of power sustained for one hour. It is commonly used to measure electrical energy consumption.

History/origin: The watt-hour is derived from the watt, the SI unit of power, and the hour, a unit of time. It was developed alongside the increasing use of electricity in the late 19th and early 20th centuries.

Current use: Watt-hours are commonly used to measure the energy capacity of batteries, the energy consumption of household appliances, and the amount of electricity generated or consumed by power plants and consumers.