The Collaborative International Dictionary of English v.0.48:

Compaction \Com*pac"tion\, n. [L. compactio.]
   The act of making compact, or the state of being compact.
   [Obs.] --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

compaction
    n 1: an increase in the density of something [syn: compaction,
         compression, concretion, densification]
    2: the act of crushing [syn: crush, crunch, compaction]

The Free On-line Dictionary of Computing (30 December 2018):

compression
compaction
uncompression

   1.  (Or "compaction") The coding of data to save
   storage space or transmission time.  Although data is already
   coded in digital form for computer processing, it can often be
   coded more efficiently (using fewer bits).  For example,
   run-length encoding replaces strings of repeated characters
   (or other units of data) with a single character and a count.
   There are many compression algorithms and utilities.
   Compressed data must be decompressed before it can be used.

   The standard Unix compression utilty is called compress
   though GNU's superior gzip has largely replaced it.  Other
   compression utilties include pack, zip and PKZIP.

   When compressing several similar files, it is usually better
   to join the files together into an archive of some kind
   (using tar for example) and then compress them, rather than
   to join together individually compressed files.  This is
   because some common compression algorithms build up tables
   based on the data from their current input which they have
   already compressed.  They then use this table to compress
   subsequent data more efficiently.

   See also TIFF, JPEG, MPEG, Lempel-Ziv Welch,
   "lossy", "lossless".

   Compression FAQ
   (ftp://rtfm.mit.edu/pub/usenet/news.answers/compression-faq/).

   Web Content Compression FAQ

(http://perl.apache.org/docs/tutorials/client/compression/compression.html).

   Usenet newsgroups: news:comp.compression,
   news:comp.compression.research.

   2.  Reducing the dynamic range of an audio signal,
   making quiet sounds louder and loud sounds quieter.  Thus,
   when discussing digital audio, the preferred term for reducing
   the total amount of data is "compaction".  Some advocate this
   term in all contexts.

   (2004-04-26)