Definitions of compression on the Web:

• compaction: an increase in the density of something
• the process or result of becoming smaller or pressed together; "the contraction of a gas on cooling"
• encoding information while reducing the bandwidth or bits required
• applying pressure
  wordnetweb.princeton.edu/perl/webwn

• In functional analysis, the compression of a linear operator T on a Hilbert space to a subspace K is the operator
  en.wikipedia.org/wiki/Compression_(functional_analysis)

• Compression, in astronomy is the deviation of a heavenly body from the spherical form, called also the ellipticity. It is numerically expressed by the ratio of the differences of the axes to the major axis of the spheroid. ...
  en.wikipedia.org/wiki/Compression_(astronomy)

• Dynamic range compression, also called DRC (often seen in DVD and car CD player settings) or simply compression, is a process that reduces the dynamic range of an audio signal. Compression is used during sound recording, live sound reinforcement, and broadcasting to control the level of audio. ...
  en.wikipedia.org/wiki/Compression_(music)

• In geology the term compression refers to the system of forces that tend to decrease the volume of or shorten rocks. ...
  en.wikipedia.org/wiki/Compression_(geology)

• In phonology, syncope (, Greek syn- + kopein “to strike”) is the loss of one or more sounds from the interior of a word; especially, the loss of an unstressed vowel.
  en.wikipedia.org/wiki/Compression_(phonetics)

• Compression (or more technically Dynamic range compression)is a subtle effect primarily for electric guitar where the highest and lowest points of the sound wave are "limited". This boosts the volume of softer picked notes, while capping the louder ones, giving a more even level of volume. ...
  en.wikipedia.org/wiki/Compression_(electric_guitar)

• Compression is the first solo album by bassist Billy Sheehan, formerly of Talas, David Lee Roth, and Mr. Big.
  en.wikipedia.org/wiki/Compression_(album)

• the act of compressing, or the state of being compressed; compaction; the cycle of an internal combustion engine during which the fuel and air ...
  en.wiktionary.org/wiki/compression

• compress - make more compact by or as if by pressing; "compress the data"
• compress - squeeze or press together; "she compressed her lips"; "the spasm contracted the muscle"
• compress - a cloth pad or dressing (with or without medication) applied firmly to some part of the body (to relieve discomfort or reduce fever)
  wordnetweb.princeton.edu/perl/webwn