Coluber is a genus of thin-bodied, fast-moving, colubrid snakes commonly known as racers. They are widespread around the world and vary greatly in habitat and behaviour. In the past, Coluber was a catch-all genus which included almost all snake species known at the time. As presented here, the genus is limited to its “modern” content of racers and whipsnakes.
More information on Racer snake can be found on Wikipedia.