Dragonball Z is an animated Japanese TV show (an anime), which has been dubbed into many languages and has become popular in many countries around the world. The English translation of the show can be somewhat clumsy and comical.
The ‘Over 9000’ meme originally came from an episode of the Dragonball Z in which Vegeta (one of the show’s ‘bad guys’) is asked "Vegeta, what does the scouter say about his power level?" and Vegeta responds "It's over 9000!". This rather nonsensical statement gained internet fame when the clip was ‘remixed’ and placed on YouTube by a fan.
‘Over 9000’ has become a phrase used to describe impressive power or skill or something that’s really awesome (or 'made of win'). For example – “That game is over 9000” or “My level of awesomeness is over 9000!”
And of course, many YouTube Videos have sprung up featuring the catchphrase in different ways including a Southpark and Myst parody.
Interestingly, in the original Japanese version, Vegeta actually says "Over 8000" but the American dubbers chose 9000 because it worked better with the lip movement of the characters on screen.
A similar clip from Dragonball Z features the character Piccolo saying "The balls are inert".