noun

• (computing) An operating system that shares the original source code by Dennis Ritchie and Ken Thompson, currently owned by Novell.
• (computing) An operating system largely compatible with Unix that qualifies for use of the UNIX trademark, currently owned by The Open Group.
• (computing, informal) Any of the above plus Unix-like operating systems similar to Unix but not qualifying for use of the UNIX trademark.
• (software) Alternative form of Unix [(computing) An operating system that shares the original source code by Dennis Ritchie and Ken Thompson, currently owned by Novell.]