A place for metal-heads, Droogies, and sometimes emos (who don't know what the hell they're doing) to congregate and basically beat the shit out of each other. Mosh pits usually take place at metal or punk concerts.
A mosh pit can, however, take place without any music. In this case a bunch of the aforementioned people would decide to gather in a public place (school, Wal-Mart, local mall, parking lot, etc.) and start an Open Pit, attempting to drag into the pit those who have no intention of entering. The most common types of mosh pits are as follows:
Confined (Closed) Pit: Involves lot's of people packed tightly together doing more jumping up and down than actual moshing. Most difficult to breathe in.
Open Pit: The most chaotic of pits, where anyone is fair game, and big slams/hits often bring congratualtions rather than reprisal. Much like a game of Wildcat
without any football pads.
Hard-Core Dance Pit: Not a true mosh pit. An open area created by some emos who have foolishly attempted to ruin everyone's good time so they can "dance." Located next to or within a real mosh pit. Involves no real dancing. Fun for real moshers to turn into an Open Pit.
Circle Pit: A mosh pit in which everyone starts running in a cicle while shoving the person in front of them. People on the outside of the pit are often thrown into the circle pit unwillingly. Anthrax has been known to encourage its fans to start a Circle Pit during live performances of the song Indians.
Charge Pit: Much like the Circle Pit, this one involves a group of people running, or "charging," through the rest of the mosh pit in ultimate disarray, running over and trampling everyone in their path, but still remaining part of the group. In my opinion, the most insane, dangerous, and fun type of mosh pit. Requires a large area and lots of people.
The Slayer concert wasn't until Friday, so Lars got some Droogies together and started a mosh pit outside Wal-Mart.
Joe tried to fuck his emo girlfriend in the Hard-core Dance Pit but got his dick torn off when the metal-heads turned it into a circle pit.
Don't get in front of the Charge Pit. The only people brave enough to start that one have steel-toed boots and the urge to kill.