9000, or OVER 9000 is a meme popularized by /b/tard and /m/oron Kajetokun (aka Kajet or Kajmaster Kajet), originating from a 13-second clip of the first season of Dragonball Z in which Nappa asks Vegeta to measure Goku's power level with his scouter. Vegeta responds "It's over NINE THOUSAAAAAANNNNNDDDD!" in a ludicrously over-the-top manner while crushing the scouter to pieces with his hand. Kajetokun created a 1:50-length parody of the scene in which the line is said repeatedly at slowed-down and sped-up tempos, with the video footage rotated to strange angles, short clips of GaoGaiGar inserted at odd times, and strategically added bleeps to make it look (at one point) like Nappa is asking Vegeta about Goku's cock.
The video is similar in concept to a relatively recent, highly popular and quite obnoxious YouTube phenomenon known as "YouTube Poop", in which episodes of animated programs and/or video game cutscenes are cut up, rearranged and played at slow and fast speeds for comedic effect (or...lack thereof). There is disagreement about whether anime-based videos qualify as YouTube Poop since the source material for those videos is usually American (or at least Western), and Kajetokun does not refer to his own videos as such; however, it should be noted 9000 was not the first video to use the technique.
On The Web
When the parody took YouTube by storm, /b/ immediately spread the meme into the other boards and later caught fire on /a/. At one point in November 2006 /a/'s entire first page had at least one "Over NINE THOUSAAANNNDDDDD!" post in every thread. An image macro of Vegeta saying "THIS THREAD IS OVER 9000" became a common way of expressing approval for a thread. The phenomenon has spread across the internet, with 9000 making it into countless webcomics, the DBZ section of Newgrounds, the Phoenix Wrong flashes and other bastions of nerd/weeaboo culture.
Kajetokun, meanwhile, has built on the success of 9000 by creating further parodies which have also achieved meme status and YouTube popularity, including I HOPE MY BODY CAN TAKE IT, The balls are inert, THE WHOLE UNIVERSE IS GOING TO DIE!, MY NINJA INFO CARDS (actually a remix of a work by another video author, KingNecroPope), ZETA PUUUNCH and the most recent, GUTSMAN'S ASS, interspersing DBZ footage with clips from GaoGaiGar, Scryed, Metal Gear Solid 2: Sons Of Liberty, Metal Gear Solid: The Twin Snakes, Tom Green's "Horseman" skits, Japanese video game commercials, MC Hammer's "U Can't Touch This" music video, Super Robot Wars, Resident Evil, Starcraft, Naruto, JoJo's Bizarre Adventure, Fist Of The North Star, Phoenix Wright: Ace Attorney, YuGiOh, StarFox 64, Megaman, Zeta Gundam and a blink-and-miss-it clip of Phantasy Star Online.
Kajetokun has also created a polka song based off of his previous videos called A Kaj-tastic Musical, The Pylons are Trap Balls. The song uses quotes from his previous videos like "Balls!" "Additional Pylons" "Trap Card" and "Vegeta" and puts to Polka as if these phrases were instruments. The end of the video also confirms that Kajetokun is indeed a /m/oron as he makes a reference to voting for Master Asia (one of /m/'s heroes) in the SaiGar contest. He also released an audio remix of MY NINJA INFO CARDS to go with the video.
Kajetokun can sometimes be found on 4chan with the phrase "not kajet" in the email field.
The English version of Dragonball Z is the only version in which Vegeta says "It's over 9000!". In the original Japanese version and all other foreign-language dubs except the English and Spanish ones, Vegeta says "It's over 8000!", although this does not necessarily mean that Goku's power level was not over 9000 in these versions. The Spanish dub says "over 10000", which arguably makes more sense given that Vegeta's scouter displays only 4 digits and thus would be incapable of giving a specific reading for a power level of over 10000. Additionally, the clip used in the parody is from the original Ocean Studios dub; in the FUNimation in-house version, Vegeta still says "It's over nine thousand!" but delivers the line in a more restrained manner, and his final lip-flap is a snarl as he crushes his scouter.