Often used with mmorpgs. It involves players banding together to succeed at a common goal- such as taking over territory, killing an opposing faction, or most commonly killing big scaryinternet monsters that drop coveted items.
It can be used as a noun or verb, noun referring a specific event, and in verbage, the act of embarking on that event.
A: We've scheduled a Black Temple raid tonight. You coming?
B: I can't raid, I gotta get laid!
A: No epix or dkp for you!
1. When the police try to shut down an illegal business that is currently in the guise of a legal business. The raid is when they finally come in to search for evidence.
A raid is when a bunch of people who play a game too much, get together to play the game some more. Because they have to work together to kill the biggest bosses.
A: What's going on, is like the whole world noobified, like the exact same time?
B: It's my guild, we are doing a raid.