Define a kilowatt hour. How is it related to joule?

One kilowatt hour is the electrical energy consumed by an electrical appliance of power 1 kilowatt when it is used for 1 hour.

1 kilowatt hour = 1 kilowatt x 1 hour
= 1000 J s^-1 x 3600 s = 3.6 x 10⁶ J