kWh = Kilowatt Hour

It is a fixed electrical unit of measurement equilvant to a fixed measurement such as 1 gallon of water.

A killowatt hour is simply a 1000 Watts of engergy consumed in one hour would equal 1 kWh (KillowattHour) 

ex. A 100Watt Light bulb burning for one hours consumes .1 kWh(Killowatt Hour)