The watt is named for the Scottish engineer and inventor James Watt (1736-1819). The watt is a unit of electric power. Wattage is also expressed in terms of watt-hours, the amount of work an appliance can accomplish. For instance, when a 60-watt light bulb operates for one hour, it uses 60 watt-hours. Meters located outside of homes generally measure electricity usage in kilowatt-hours.