Foam consists of a mass of small bubbles that are formed when air and a liquid are mixed together.

Foam is used to refer to various kinds of manufactured products which have a soft, light texture like a thick liquid.

Foam or foam rubber is soft rubber full of small holes which is used, for example, to make mattresses and cushions.

If a liquid foams, it is full of small bubbles and keeps moving slightly.

If you say that someone is foaming at the mouth, you mean that they are very angry.