Compression

[1] Applying pressure to a spring, or any springy substance, thus causing it to reduce its length in the direction of the compressing force.
[2] Applying pressure to a gas, thus causing a reduction in volume.
[3] One of the essential factors in a internal combustion engine (fuel, air, proper proportion of mixture, compression, timing, spark). It is the squeezing of the fuel-air mixture in the cylinder of a spark-ignition engine or the squeezing of the air in a diesel engine. Compression makes the process of combustion more effective and increases engine efficiency.
[4] Term used to denote increase of pressure on a fluid by using mechanical energy.
[5] Reduction in volume and increase in pressure and temperature of a gas caused by squeezing it into a smaller space
See also crankcase compression, grooved compression ring, high compression head, piston ring, compression, primary compression ratio, primary compression, ring, compression, secondary compression