Subspecies may be thought of as geographic races. A race is a population or group of populations in a species which inhabits a particular geographic area and has gene frequencies that are different from other races in the species. Phenotypic traits also may differ among races, and the races of one species are capable of interbreeding with one another. Lack of concordance in distinguishing characteristics often leads to distinctions based on one trait, rather than a number of traits. Taking things to an extreme, some combination of characters potentially could distinguish every population from all others.
Polytypic species are species which are divided into subspecies.
There are many potential examples. Clines A cline is a gradual change in a characteristic along a geographical transect. Clines may extend across the entire geographic range of a species. A step cline is a short, steep cline between two widespread forms within a species, sometimes between subspecies. The colors and patterns differ greatly among subspecies.