an Open Group Specification that is compatible with Version 1 of the Single UNIX Specification, a standard Unix programming interface that governs compliance. It was published in 1994, supplanting UNIX 93, which was not compliant with the Single UNIX Specification.
Unix is an operating system (OS) formulated in 1969 at Bell Labs as an interactive time-sharing system. It was never a proprietary OS and is not owned by either of the leading computer companies.
Version 2 of the Unix specification is called UNIX 98. It added support for real-time processing threads, Y2K compliance and architecture neutrality. It was followed by UNIX 03.