To store data in a compact form in a storage medium by taking advantage of known characteristics of the data and the storage medium, in such a way that the original form of the data can be recovered, e.g, to make use of bit or byte locations that would otherwise go unused.
Because a laser beam does not diverge, it carries its energy in a very compact form.
Data in bits can often be recorded into a more compact form for transmission, using a compaction algorithm. A related algorithm can recover the original form ; the entire sequence represents companding.
