Unix is the name of an operating system. And unix is a registered trademark. This is what makes things murky.
One of my favorite books is The Design and Implementation of the 4.3BSD UNIX Operating System. That book is out of print, but a newer book is available: The Design and Implementation of the 4.4BSD Operating System. Note that "UNIX" was dropped from the title. BSD no longer has the legal right to call itself UNIX. It's not alone. Linux has never had the legal right to call itself UNIX.
There is a set of operating systems that includes Solaris, HP-UX, AIX, Linux and BSD among several others. We can't legally call that set, um, you-know-what. But understand that Linux is not out in left field. It is a co-equal member of that set.
We have a lot of threads that shed more light....
Don't hate me because I'm stupid...
A short history of UNIX by l.madden@ic.ac.uk
what is unix?
Just curious, does Unix stand for anything?
Click here for the best unix in the world!!!!
SCO sues IBM
Halloween IX: It Ain't Necessarily SCO
GNU and Linx: Different or the same?
The history of UNIX and the ideas behind it