com·pres·sion 
(kəm-prĕshən)
(kəm-prĕshən)n.
1.
a. The act or process of compressing.
b. The state of being compressed.
2.
a. The process by which the working substance in a heat engine, such as the vapor mixture in the cylinder of an internal-combustion engine, is compressed.
b. The engine cycle during which this process occurs.
3. Computers The process by which data is compressed into a form that minimizes the space required to store or transmit it.
com·pression·al adj.