Foam/fəʊm/ Definition 1 of 4Pro Tip 1/3Natural Occurrence Foam often describes natural bubbles, typically seen with water or other liquids. The river's rapids created foam along the edges. Pro Tip 2/3By-product of Action Foam can occur because of an action like shaking a liquid. He shook the soda bottle, and foam erupted when opened. Pro Tip 3/3Visual Description Foam is a visual term often used to describe a white bubbly appearance. A layer of foam coated the top of the hot latte.