Blow a stream of bubbles. What is a bubble? Bub-ble.Noun. 1 A thin, usually spherical or hemispherical film of liquid with air or gas: a soap bubble. 2 A globular body of air or gas formed within a liquid: air bubbles rising to the surface. 3 A pocket formed in a solid by air or gas that is trapped, as during cooling or hardening. 4 a. The act or process of forming bubbles. b. A sound made by or as if by the forming and bursting of bubbles. The toy association.