At the beginning...

Unix was originally developed in AT&T at the late 60s/early 70s. Their version (beginning at 1982) is called System V Unix (or SysV for short).

The system was initially a research project, with a limited distribution (it only went out of Bell Labs past 1976).

As a counter-movement, the California university in Berkeley creates its own version of Unix, called BSD Unix, and releases it under the BSD software license, in 1983. However, it contains AT&T SysV sources, and is thus not really free. Later, a release with no AT&T source code would be created.