A kilowatt-hour (kWh) is a unit of energy that measures how much electricity is used over time. It represents the amount of energy consumed when a device with a power rating of one kilowatt operates for one hour. For example, if a light bulb uses 100 watts, it would take 10 hours of use to consume one kWh. Electricity bills often show usage in kWh, helping consumers understand their energy consumption. Knowing how many kWh are used can assist in managing energy costs and promoting energy efficiency in homes and businesses.