1. Usually made of dairy products including eggs... is often chocolate flavoured.
2. Sometimes has gelatin/gelatine as an ingredient (not edible for vegetarians!)
3. Usually served as a cold dessert, decorated with berries or chocolate shavings.

Mousse is a dairy based dessert. Not to be confused with the animal, 'moose'! There is also another type of 'mousse', which is a hair product - used like gel to achieve a certain hairstyle. Of course this is different from the type of mousse you would eat!