Whipped cream is fresh sweet cream (often with sugar and vanilla added) that is whipped with a device such as a blender until it is semi-soft or somewhat stiff. Whipped cream is kept chilled to refrigerator temperatures throughout the process, usually by making it in a chilled bowl.
Clotted cream is prepared by heating the cream for up to an hour with very hot water or steam. This alters the casein (milk protein) in the cream, which thickens the cream into a dense substance. Clotted cream is more cheeselike in texture and less airy than whipped cream.
Whipped cream is popular in the US, and clotted cream in England. If you want to write about this, check Wikipedia - the information there was helpful.