Definition - What does UNIX 03 mean?
UNIX 03 is an Open Group Specification first appearing in 2002, which was later approved in 2003. It is comprised of the IEEE portable operating system interface for Unix (POSIX) and Single UNIX Specification, version 3. UNIX 03 is the most recent update to the UNIX product standard family since 1997.
Techopedia explains UNIX 03
UNIX is an 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. UNIX also is written in a standard language and is comprised of many popular ideas, which led UNIX to become the primary available open standard OS.