<p><strong>noun</strong></p><ul><li>a collection of minute bubbles formed on the surface of a liquid by agitation, fermentation, etc.: foam on a glass of beer.</li><li>the froth of perspiration, caused by great exertion, formed on the skin of a horse or other animal.</li><li>froth formed from saliva in the mouth, as in epilepsy and rabies.</li><li>a thick frothy substance, as shaving cream.</li><li>(in firefighting) a chemically produced substance that smothers the flames on a burning liquid by forming a layer of minute, stable, heat-resistant bubbles on the liquid's surface.</li><li>the layer of bubbles so formed.</li><li>a dispersion of gas bubbles in a solid, as foam glass, foam rubber, polyfoam, or foamed metal.</li><li>Literary. the sea.</li></ul><p><strong>verb</strong></p><ul><li>(used without object) to form or gather foam; emit foam; froth.</li><li>(used with object) to cause to foam.</li><li>to cover with foam; apply foam to: to foam a runway before an emergency landing.</li><li>to insulate with foam.</li><li>to make (plastic, metal, etc.) into a foam.</li></ul>