Pronunciation: (kum-presh'un),[key] —n. 1. the act of compressing.
2. the state of being compressed.
3. the effect, result, or consequence of being compressed.
4. (in internal-combustion engines) the reduction in volume and increase of pressure of the air or combustible mixture in the cylinder prior to ignition, produced by the motion of the piston toward the cylinder head after intake.
5. reduction of the size of computer data by efficient storage. Also,com•pres•surePronunciation: (kum-presh'ur)[key](for defs. 1, 2).