What is Foam ?
Foam is (noun) a mass of small bubbles This detergent makes a huge amount of foam. (verb) to make a mass of small bubbles The waitress was carrying mugs of foaming beer. The horse was foaming at the mouth after the race. to be foaming (at the mouth) (of a person) to be extremely angry The MD was foaming (at the mouth) when he read the report in the paper.
source: Easier English, Student Dictionary Upper Intermediate Level