from Wiktionary, Creative Commons Attribution/Share-Alike License
- proper n. A computer operating system that shares the original source code by Dennis Ritchie and Ken Thompson, currently owned by Novell.
- proper n. An operating system largely compatible with Unix that qualifies for use of the Unix trademark, currently owned by The Open Group.
- proper n. A Unix-like operating system similar to Unix but not qualifying for use of the Unix trademark.
- proper n. The group of Unix operating systems as a whole.
A pun on Multics; coined by Brian Kernighan. (Wiktionary)