compression

Short definition from Wiktionary

Noun

1. 1
   An increase in density; the act of compressing, or the state of being compressed; compaction.
2. 2
   The cycle of an internal combustion engine during which the fuel and air mixture is compressed.
3. 3
   The process by which data is compressed.
4. 4
   The electronic process by which any sound's gain is automatically controlled.
5. 5
   The deviation of a heavenly body from a spherical form.