The Blur is a name used on Smallville for Clark Kent's superheroics before he became known to the world as Superman. The name started as a literal description by eyewitnesses to an unseen protector on the streets of Metropolis: the Red-Blue Blur. This was at a time when Clark would regularly wear a blue shirt with a red jacket. After he started wearing black, the media redubbed him "The Blur".
The Blur as a designation for Clark Kent before becoming Superman is original to Smallville. However, it has been alluded to in the comics. In Superman/Batman #73 (August 2010), a close-up shot of Lois Lane researching on her computer, shows a newspaper headline in the background that reads, "RED-BLUE BLUR" GETS A NAME.