A watt is the SI unit for power. A watt is equal to 1 Joule per second , or (energy in an amount of time). A watt of power is about equivalent to a person holding out their arm and moving their fist up and down each second.
Deep knee bends output about 100 W of power. This is about the average total power input of a person over a normal day, which is why R. Buckminster Fuller came up with the idea of this calling this an energy servant. Since it's actually a unit of power, this site discusses them as power servant.
For more information on the watt, click here.