Mousse is a form of creamy dessert typically made from egg and cream (classically no cream, only egg yolks, egg whites, sugar, and chocolate or other flavorings), usually in combination with other flavors such as chocolate or pureed fruit. The egg whites are beaten before being incorporated into the other ingredients to produce a light and fluffy yet extremely rich confection. It is then chilled to maintain its aeration.
Once only a specialty of French restaurants, chocolate mousse entered into American and English home cuisine in the 1960s. Mousse-like desserts in middle America commonly go under designations like "whip".
Depending on how it is prepared, it can range from light and fluffy to creamy and thick.
Due to usage of raw eggs, eating mousse may lead to food poisoning, caused by salmonella bacteria. Note that in the UK eggs marked with the Lion Mark have come from hens vaccinated against salmonella, although they may not have been pasteurized; but catering establishments generally use pasteurized eggs. Most food service establishments in the U.S. use pasteurized eggs whenever raw eggs are called for, so food poisoning should not be a concern there except in home cooking.
"Bavarian cream" (Fr. Bavaroise) is similar to mousse.