1. An archiver that is used to combine many files and directories in single archive file. The name comes from 'Tape ARchive', since the utility was created to make tape backups of Unix systems. From Linux Guide @FirstLinux

2. A program used to create a single file archive from several files, often used to distribute programs for Unix. The Unix command has many options. From KADOWKEV

3. GNU tar Tar is a program for packaging a set of files as a single archive in tar format. The function it performs is conceptually similar to cpio, and to things like pkzip in the DOS world. It is heavily used by the Debian package management system, and is useful for performing system backups and exchanging sets of files with others. From Debian 3.0r0 APT

4. The GNU tar program saves many files together into one archive and can restore individual files (or all of the files) from the archive. Tar can also be used to add supplemental files to an archive and to update or list files in the archive. Tar includes multivolume support, automatic archive compression/decompression, the ability to perform remote archives and the ability to perform incremental and full backups. If you want to use Tar for remote backups, you'll also need to install the rmt package. You should install the tar package, because you'll find its compression and decompression utilities essential for working with files. From Mandrake 9.0 RPM