Cavitation
Definition
When low pressure boils water cold — collapsing vapor bubbles that chew up boat propellers and pumps.
Technical definition
Where local pressure drops below vapor pressure, vapor cavities form; their violent collapse produces shock waves, noise, and erosion.
Example
Submarine propellers are shaped to avoid cavitation — the collapsing bubbles are deafeningly loud underwater and would betray the boat's position.
Common confusion
Cavitation bubbles contain vapor, not air. They form from pressure drop, not heating — boiling without heat is the entire point.