It's the name given to a mash-up based on a scene from the 2007 movie 300. It is a specific kind of remix that requires perfect timing.
Someone who makes sparta remixes is a Sparta Remixer. Sparta Bases is simply the instrumental base (or backing track) of a Sparta remix. Someone who makes sparta bases is a Sparta Base Maker.
Keaton, the creator of the sparta remix, released his 300 This is Sparta (fun times mix) in 2007. He posted it on YTMND where it gained considerable popularity. But the fad really didn't start until he decided to extend his remix, and the EXTENDED fun times mix was put in several videos containing Sparta gifs and memes at that time. The tempo of 95% of Sparta Bases is 140 BPM. The tempo of the other 5% of bases, such as the Hyper LOL Base by GringoHisopo1993, is 150 BPM.
It is largely criticized by YTPMVers because it its repetitive.
Main Article: History of the Sparta Remix
These are the components that makes a Sparta Remix.