What is the difference between kW and kWh?

The difference between kWh and kW is that a kWh reflects the total amount of energy used, whereas a kW reflects the rate of energy usage (which is technically called power). So, if you have five 40W lightbulbs on for 3 hours, they will consume 600 Wh of energy (which is 0.6 kWh) during that period.