"Foam" means enclosing a gas with a liquid, which is Sanzui, but in the world of engineering, "foam" and "air bubbles" must be clearly distinguished. As shown in the figure below, due to the interrelationship between gas and the liquid that surrounds it,
[foam] = [surface foam]
[bubble] = [dispersion foam]
Surface foam (FOAM) floating on the liquid surface and dispersed It is classified as BUBBLE.