In electrical usage terms, Watts is the unit of measure for the Real Power (also referred to as Active Power) dissipated or drawn by a connected load. Some Unity power factor rated uninterruptible power supplies use Real Power for their rating.
Real Power (W) = Supply Voltage (V) x Amps (A)
For three phase loads, the Real Power is calculated for each individual phase and the three results added together to give a final total three phase Real Power result.