Suds are the foamy bubbles that form when soap or detergent mixes with water. When you wash your hands and work the soap into a lather, those white, fluffy bubbles covering your skin are suds. The more you rub and agitate soapy water, the more suds you create.

Suds form because soap molecules trap tiny pockets of air inside thin films of water. When you squeeze a dish sponge full of suds, you're actually crushing thousands of these tiny bubbles. In a bathtub, suds can pile up into mountains of foam. Some dishwashing liquids or shampoos produce more suds than others, though lots of suds doesn't necessarily mean something cleans better.

People sometimes use the word informally to mean soapy water in general, like when someone asks you to “rinse the suds off the car” after washing it. You might also hear someone say they're “in the suds” when they're washing dishes, meaning they're elbow-deep in soapy, bubbly water.