The diamondback terrapin (Malaclemys terrapin) or simply terrapin, is a species of turtle native to the brackish coastalswamps of the eastern and southern United States. It belongs to the monotypic genus, Malaclemys. It has one of the largest ranges of all turtles in North America, stretching as far south as Florida Keys and as far north as Cape Cod.
The name “terrapin” is derived from the Algonquian word torope.It applies to Malaclemys terrapin in both British Englishand American English. The name originally was used by early European settlers in North America to describe these brackish-water turtles that inhabited neither freshwater habitats nor the sea. It retains this primary meaning in American English. In British English, however, other semi-aquatic turtle species, such as the red-eared slider, might be called a terrapin. source