An interrogative as to the events that have come to play, be it in the distant past, the recent past, or the present. This phrase may or may not use a question mark, but is an interrogative, regardless.
This phrase, popular among geeks, alludes to the poorly-translated Sega game Zero Wing; however, it is not always used for its pop culture value alone.
person: "Oh shit."
person2: "what happen"
person: "My term paper got deleted from my computer!"
person2: "Seriously? Oh, shit! Are you sure there isn't a back up somewhere?"
person: "Nope, not one back-up."
person2: "All your docs are belong to trash :("
1) a question when one is curious about what is going on around him.
2)A popular greeting greating used instead of "hello".
3) A state of confusion when used in a situation where both definitions intertwine.
eg. when you have just met someone whom you know and who may be curious about a situation or the goings on around you.
Literally: "what happened?" Comes from some Japanese video game in a poor English translation. See also: all your base are belong to us, someone set up us the bomb, make your time, et al.