- A computer operating system that shares the original source code by Dennis Ritchie and Ken Thompson, currently owned by Novell.
- An operating system largely compatible with Unix that qualifies for use of the UNIX trademark, currently owned by The Open Group.
- (informal) A Unix-like operating system similar to Unix but not qualifying for use of the UNIX trademark.
- GNU is not Unix.
- The group of Unix operating systems as a whole.
- The Linux kernel operating system is one of the most popular forms of Unix.
- (computer operating system): *nix