A compressor is a mechanical device that increases the pressure of a gas by reducing its volume. It works on the principle of conservation of mass and energy, which states that the total amount of mass or energy in an isolated system remains constant. Compressors are widely used in various applications such as air conditioning systems, refrigerators, and engines to increase the pressure of gases so they can be transported through pipelines or stored at high pressures. There are many types of compressors including reciprocating, rotary screw, centrifugal, and axial flow compressors, each with its own specific design and application.