It's over 9000! is a popular internet meme originating from the popular anime "Dragon Ball Z".
Development
In the original Japanese version, Vegeta's line was "It's over 8000!". This was changed in the dub to match Vegeta's lip movement during this bit of dialogue.
Fan Use
The line has been used in various forms of media, to show when there is a large amount of something.
Use in Popular Culture
In the visual novel game "Phoenix Wright: Ace Attorney", the character Sal Manella uses the phrase.