Stereotypical home for the geek, nerd, fatbeard, loser, etc. The term implies that the individual still lives with one or both of his parents despite being a grown man. Reasons for still living at home may include a lack of drive and ambition, being unable to afford a place of his own due to spending all of his money on his hobbies (i.e. Star Trek figurines, comic books, and online role-playing games), or just plain being a mama's boy.
"Jeff is such a loser. He really needs to move out of his mom's basement and work on getting laid rather than spending every free minute playing World of Warcraft."
by You Can't Kill the Metal September 10, 2006