Web Definition: BSD - Berkeley Software Distribution. Implementation of the UNIX operating system and its utilities developed and distributed by the University of California at Berkeley. BSD is usually preceded by the version number of the distribution, e.g., 4.3 BSD is version 4.3 of the Berkeley UNIX distribution. Many Internet hosts run BSD software, and it is the ancestor of many commercial UNIX implementations.
www-rohan.sdsu.edu/glossary.html
Google explained it better than i could
Edit: Also in Mac OSX there is a BSD type core running under Apples GUI.
And you probably wont be able to run most windows exe files, you could use WINE (Wine Is Not an Emulator) that allows some major programs (like Office/photoshop) to run on linux/BSD, but it's a pain to setup for newbies usually.