1. A mass of small bubbles formed in or on a liquid
   "the beer had a thick head of foam";
   - froth
    
2. A lightweight material in cellular form; made by introducing gas bubbles during manufacture
   "The packaging was filled with protective foam"

1. Become bubbly, frothy or foaming
   "The river was foaming";
   - froth, fizz, effervesce, sparkle, form bubbles

Derived forms: foamed, foams, foaming

Type of: bubble, material, stuff

Encyclopedia: Foam