Define commercial unit of energy

The commercial unit of energy is given as kWh or kilo-watt-hour.

It is defined as the work done at a rate of 1000 Watt in a time of one hour.

there are other units of energy also like joules, calories but they are not big enough to express large quantity of energy. that is why we use kWh as the commercial unit since it is bigger compared to other energy units.