Compressed file archive. Tar is a UNIX method of archiving files, which can also be used by PCs. Tar archives files but does not compress them, so sometimes .tar files are compressed with other utilities, which produces extensions like .tar.gz, .tar.Z, and .tgz. Archive files with the .tar extension can be extracted in UNIX with tar or on a PC with WinZip or on the Mac with the program Tar.