The formation of an air or vapor pocket (or bubble) due to lowering of pressure in a liquid. Often the result of a solid body, such as a propeller or piston, moving through the liquid. Cavitation can occur in a hydraulic system as a result of low fluid levels drawing air into the system. This produces tiny bubbles that expand explosively at the pump outlet causing metal erosion and eventual pump destruction.
Tip excerpted from: The Professional's Guide to Maintenance and Reliability Terminology by Ramesh Gulati, Jerry Kahn and Robert Baldwin