Smallville is the name of a small rural town located in New York which is home to the Kent family. It is often the place where the Kryptonian rocket containing baby Kal-El lands, and the town in which Clark Kent grew up.
The town first appeared as "Smallville, USA" in Superboy (volume 1) #2 (1949). "Smallville, USA" is also a generic term to describe a relatively small American community, which is rural in nature. This in direct contrast to Metropolis, which is meant to display an urban American area that is highly populated and well-known.