Froth is a mass of small bubbles on the surface of a liquid.

If a liquid froths, small bubbles appear on its surface.

If you say that someone is frothing, or that they are frothing at the mouth, you are emphasizing that they are very angry or excited about something.

If you refer to an activity or object as froth, you disapprove of it because it appears exciting or attractive, but has very little real value or importance.