gzip GNU Zip is a file compression format which the GNU project invented because Unix's compression tool 'compress' was Proprietary software. (It used the LZW algorithm, which Unisys claimed was covered by one of their patents after the algorithm was in wide-spread use). As is often the case1?, it was better than the proprietary program which it was designed to replace.

See gzip(1), gunzip(1).

1? fiasco (a non-proprietary reimplementation of L4, Linux (as opposed to UNIX),