BSD (Berkeley Software Distribution), sometimes called Berkeley Unix, it is the Unix operating system developed and distributed by the Computer Systems Research Group (CSRG) of the University of California, Berkeley, from 1977 to 1995.
Historically, BSD has been considered as a branch of UNIX — "BSD UNIX", because it shared the initial codebase and design with the original AT&T UNIX operating system.
The final release from Berkeley was 1995’s 4.4BSD-Lite Release 2, after which the CSRG was dissolved and development of BSD at Berkeley ceased. Since then, several variants based directly or indirectly on 4.4BSD-Lite (such as FreeBSD, NetBSD, OpenBSD and DragonFly BSD) have been maintained.