<tool, compression> GNU compression utility. Gzip reduces the size of the named files using Lempel-Ziv LZ77 compression. Whenever possible, each file is replaced by one with the filename extension ".gz". Compressed files can be restored to their original form using gzip -d or gunzip or zcat.
The Unix "compress" utility is patented (by two separate patents, in fact) and is thus shunned by the GNU Project since it is not free software. They have therefore chosen gzip, which is free of any known software patents and which tends to compress better anyway. All compressed files in the GNU anonymous FTP area (gnu.org/pub/gnu) are in gzip format and their names end in ".gz" (as opposed to "compress"-compressed files, which end in ".Z").
Gzip can uncompress "compress"-compressed files and "pack" files (which end in ".z"). The decompression algorithms are not patented, only compression is.
The gzip program is available from any GNU archive site in shar, tar, or gzipped tar format (for those who already have a prior version of gzip and want faster data transmission). It works on virtually every Unix system, MS-DOS, OS/2 and VMS.