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".
Comics[]
The Blur as a designation for Clark Kent before becoming Superman is original to Smallville. In the comics, Superman/Batman #73 (August 2010) features a close-up shot of Lois Lane researching on her computer, with a newspaper headline in the background: "RED-BLUE BLUR" GETS A NAME.
Superman being seen as a "blur" — a thing that cannot be seen or heard clearly — is a reference to his great speed. The term has been used as a noun to describe Superman on many occasions, such as Superman #29 (1939), "The Pride of Kents."