The term "watt" is derived from English inventor James Watt. It is a unit of power, used to measure radiant flux. The watt is a derived SI unit, meaning it is defined in terms of two more base SI units. In terms of base units, one watt can be expressed as:

W = m^{2}·kg·s^{-3}

A simpler definition, in terms of a non-base unit, would be:

W = J/s

Basically what this means is that one watt is the amount of work done by applying one joule of energy per second. Alternately, you could also say that the watt is the power produced by one ampere of current across a potential difference of one volt in an electric circuit.

**Conversions:**

1 W = 1 J/s =

0.000947817144 Btu/s
0.0568690286 Btu/min
3.41214172 Btu/hour
0.0000341214172 therms/hour
0.238845897 calories/s
14.3307538 calories/min
0.000238845897 kilocalories/s (Calories/s)
0.0143307538 kilocalories/min
0.859845228 kilocalories/hour
0.00134048257 horsepower (electric)
0.00135962162 horsepower (metric)
0.06 kilojoules/min
0.0036 megajoules/hour
0.101971621 kgf·m/s^{*}
0.737562149 foot·lbf/s^{**}

^{*} kgf·m is kilogram-force meter

^{**} foot·lbf is foot pound-force

Conversions courtesy of: http://www.ex.ac.uk/cimt/dictunit/ccpower.htm