Watt n. : A unit of power or activity equal to 107 C.G.S. units of power, or to work done at the rate of one joule a second. An English horse power is approximately equal to 746 watts.

Example:
How many Watts does the amp have to have for an 800 Watt subwoofer?

Taxonomy
watt, megawatt, MW, kilowatt, power, quadrillion watts, the International, energy, nanowatt, gigawatt, terawatt, electrical, kilowatt-hours, power plants, watt bulb, free encyclopedia, Symbol, speed.

Defination from the web:
watt is equivalent to 1 joule (J) of energy per second. In terms of mechanical energy, one watt is the rate at which work is done when an object is moved at a speed of one meter per second against a force of one newton. ...