The kilowatt-hour (symbolized kWh) is a unit of energy eqivalent to one kilowatt (1kW) of power expended for one hour of time.  It is the standard measure of electrical energy and the typical billing unit used by electrical utilities for electricity use.

For example, a 100-watt lamp operated for 10 hours consumes 1000 watt-hours (100 x 10) or one kilowatt-hour. If the utility charges $.10/kWh, then the electricity cost for the 10 hours of operation would be 10 cents (1 x $.10).  The average annual electrical energy consumption of a household in the United States is about 8,900 kilowatt-hours, equivalent to a steady power consumption of about 1 kW for an entire year.