Probably a turtle, they are more numerous than the few species of North American land tortoises. Terrapin... lol... That's a trigger word that usually starts a flamewar over at Turtle Forums.
Here is what Wiki says (but some folks disagree):
Taxonomy -
Although sometimes superficially similar to sea turtles in shape, having webbed feet and thinner shells than fully terrestrial tortoises, terrapins do not belong to the sea turtle superfamily Chelonioidea. In British English, the species most commonly referred to as terrapins are members of the family Emydidae including the red-eared slider (Trachemys scripta elegans) and the slider terrapin (Trachemys dorbignyi). Perhaps confusingly, although the genus to which the box turtles belong, Terrapene, sounds similar to the word terrapin, these turtles are not normally called terrapins.
Usage of the name "terrapin" in British and American English compared -
Different animals are called turtles, tortoises, or terrapins in different varieties of English
The name "terrapin" is unambiguously applied to the diamondback terrapin (Malaclemys terrapin) in both British English and American English; the name originally being used by early European settlers in North America to describe these brackish water reptiles that inhabited neither freshwater habitats nor the sea. However, in American English the name is not routinely applied to other semi-aquatic or freshwater turtles, unlike the situation in British English where any such turtle might be called a terrapin.
