What is an XBOS?

XBOS is an acronym standing for "X-Based Operating System". This refers to the X in UNIX, MINIX, Linux, and OSX (a FreeBSD UNIX variant). Solaris is an XBOS too, even though it doesn't have an "X" in its name; it is an X-Based OS, after all.

Where did the acronym come from?

To my knowledge, I coined this term during development of NMOX.