Berkeley Software Distribution

Berkeley Software Distribution (BSD) is an operating system derived from Unix, originally developed for the  and  under the direction of  at the University of California, Berkeley. BSD Unix has subsequently been ported to almost all modern general-purpose computer architectures and incorporates paged virtual memory, TCP/IP networking enhancements and many other features.

History
BSD UNIX 4.0 was released on October 19, 1980. The BSD versions (4.1, 4.2, and 4.3) and the commercial versions derived from them held the technical lead in the Unix world until AT&T's successful standardization efforts after about 1986, and are still widely used. The underlying kernel of Mac OS X (now macOS) and Darwin can be traced back through NeXTSTEP as a modified derivative of BSD Unix.