Watts is a metric unit of power. One horsepower = 746 watts. In the United States it is mostly used to measure electrical power but in the rest of the world, the power of gas engines is also rated in watts or kilowatts.

The definition of a watt is one newton of force x one meter per second. There is a common misperception that electrical units define the watt. Instead, the watt is used to define the volt. The definition of a volt is the amount of electrical potential that caused one amp of current to deliver one watt of power, thus you can measure watts by multiplying amps times volts, as long as you are dealing with direct current. Things get a little more complicated with alternating current and a non resistive load.