Some people told me FreeBSD is NOT Unix, is that right? Confused

It all come down to whether you are speaking legally, or from a technology viewpoint. Legally, FreeBSD, like Linux, cannot use the trademarked term Unix. From a technology point of view, FreeBSD is as much Unix as Solaris, HP-UX, or any of the other commercial versions that have paid to be able to be legally called Unix.

The word Unix is actually a trademark name that refers to System V Unix. So "legally" it is not Unix. But it is related and "looks" like Unix, so it is often called Unix, or Unix-like. http://en.wikipedia.org/wiki/Unix

Legally, something is allowed to call itself "Unix" if it goes through an expensive certification process by X/Open. So no, FreeBSD is not Unix, they wouldn't dream of squandering the little cash they have to go through a multi-year certification that is obsolete the moment they get it (one change, start over). On the other hand, all the BSDs are direct decendents of the original Unix source code from AT&T, hacked beyond recognition by a horde of enthusiasts from all over the world. So yes, FreeBSD is a (genetic) Unix. In the same way, Linux is not Unix, neither legally nor genetically. But Linux was conceived as a faithful workalike of what Unix is all about (it closely follows POSIX), so, yes, Linux is also Unix.

Confused enough? ;-)