# BSD

Wikipedia has an article about:
BSD 

RogueBasin has a wiki page about:
BSD 

BSD is an acronym for Berkeley Software Distribution, a flavor of Unix operating system that reigned in the 1970s and 1980s. Today, the term BSD (or *BSD) refers to one of its modern derivatives: usually FreeBSD, NetBSD or OpenBSD. To this day, NetBSD continues the custom of including Rogue, Hack and Larn in the system.
You can run NetHack on BSD, but the situation has changed so much since then that some will "#define SYSV" and "/* #define BSD */" in config.h. 
Another descendant of BSD is Darwin, the base system of Mac OS X. The NetHack TTY and X11 ports run on it.