Foamy describes something covered with or full of foam: light, airy bubbles that form on top of liquids. When you pour root beer too fast, it gets foamy at the top. When waves crash on the beach, they leave foamy white surf on the sand. A cappuccino has a thick, foamy layer of steamed milk on top.

Foam forms when air gets trapped in tiny bubbles within a liquid. Shampoo becomes foamy when you work it through your hair because you're mixing air into it. The same thing happens when you whip cream: it transforms from liquid to a thick, foamy topping as air bubbles get trapped inside.

The word can describe textures beyond liquids too. Certain materials feel foamy because they're light and full of air pockets, like the foam padding in a bike helmet or the foamy cushions on your couch. Scientists even talk about “foamy” structures in nature, like certain kinds of lightweight volcanic rock that hardened while full of gas bubbles.

When something is especially foamy, you might say it's frothy, which means almost the same thing but suggests even more bubbles and lightness.