Real Dictionary

mousse
variable noun: Mousse is a soft substance containing a lot of tiny bubbles, for example one that you can put in your hair to make it easier to shape into a particular style.
variable noun: Mousse is a sweet light food made from eggs and cream. It is often flavoured with fruit or chocolate.

mousse in American English
any of various light chilled or frozen foods made with egg white, gelatin, whipped cream, etc., combined with fruit or flavoring for desserts, or with fish, meat, etc.
to shape or style (hair) with mousse
noun: a sweetened dessert with whipped cream as a base, often stabilized with gelatin and chilled in a mold

mousse in British English
noun: a light creamy dessert made with eggs, cream, fruit, etc, set with gelatine