A family of Unix version operating systems developed around 1980 by Bill Joy and others at Berkeley (or "Berzerkeley," which was said to be known for BSD and LSD). Incorporating paged virtual memory, TCP/IPnetworking enhancements, and many other features, the BSD versions 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. BSD is still widely popular, and it is credited with establishing the Internet in colleges and universities since it included TCP/IP. The little dude above is the Berkeley daemon ;-)
FYI: "BSD licenses" represent a family of permissive free software licences, which have few restrictions compared to other free software licenses (such as the GNU GPL or even the default restrictions provided by copyright). Since BSD licenses are closer to the public domain, they have been referred to as "copycenter" as a comparison to standard copyright and copyleft free software.