Incipient Cavitation

The pump curve that came with your pump shows the net positive suction head required (NPSHR) for any given impeller size and capacity.

This number was determined by pumping cold water through the pump while reducing the suction head until the pump showed a reduction in discharge head of three percent (3%), due to the low suction head and any formation of bubbles within the pump.

This point is called "the point of incipient cavitation".