Pumps are devices that use mechanical energy to increase the velocity, pressure, or elevation of liquids and gases. There are two main types of pumps: positive displacement pumps and dynamic pumps. Positive displacement pumps apply pressure directly to the fluid using reciprocating or rotating components like pistons, plungers, or gears. Dynamic pumps like centrifugal pumps use an impeller to impart kinetic energy and convert it to pressure energy. Key factors in pump performance include head, which measures pressure energy, and net positive suction head (NPSH), which must be sufficient to prevent cavitation damage to the pump.