The BSD (Berkeley Software Distribution) is a UNIX operating system developed by University of California at Berkeley during the 70s and 80s.
The Berkeley Software Distribution, usually known as BSD, is a UNIX operating system developed by University of California at Berkeley during the 1970s and 1980s. It lives on in several projects: the “big three” freebsd, netbsd, openbsd, as well as others such as dragonfly-bsd, pc-bsd, …
Unless your question is about historic systems or about features shared by all BSDs, you should tag it with the proper specific tag (freebsd, …) instead of bsd.