compress: A tool found in UNIX systems. It produces a .Z file that contain a lossless encoding of data in another file into the LZW format. (An explanation of LZW can be found here.) Thanks to the actions of Unisys, who owns the patent on LZW, and to the rise of free UNIX clones such as BSD and GNU/Linux, compress is on its way out, in favor of more efficient, non-patented tools such as gzip and bzip2.