a lightweight material in cellular form; made by introducing gas bubbles during manufacture
"The architect chose foam insulation because its lightweight, cellular structure makes it easy to install and highly effective at trapping heat."
A substance composed of a large collection of bubbles or their solidified remains.
"The ocean churned into white foam as the massive waves crashed against the rocky shore, leaving behind a layer of frothy residue that slowly dissipated in the wind."
In plain English: Foam is bubbly stuff that forms on top of liquids when they are agitated, like soap suds or sea spray.
"The beer in his glass had a thick layer of white foam on top."
Usage: Use foam to describe any bubbly mass, whether it is the light layer on top of your coffee or hardened volcanic rock. Avoid confusing this with "froth," which typically refers only to small, short-lived bubbles in liquids like beer or soda.
become bubbly or frothy or foaming
"The boiling soup was frothing"
"The river was foaming"
"sparkling water"
To form or emit foam.
"The agitated water began to foam at the edges of the bathtub as I turned on the showerhead."
The word foam comes from Old English and originally meant the same thing it does today. It traveled into modern usage through Middle English without changing its core meaning of bubbly liquid or froth.