foam

(noun) a mass of small bubbles formed in or on a liquid. Synonyms: froth. Example: "The beer had a thick head of foam."

(noun) a lightweight material in cellular form; made by introducing gas bubbles during manufacture.

(verb) become bubbly or frothy or foaming. Synonyms: froth, fizz, effervesce, sparkle, form bubbles. Examples: "The boiling soup was frothing." "The river was foaming." "Sparkling water."