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.
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. A terrapin is the mascot of the University of Maryland and Tampa Preparatory School.
The Grateful Dead's 1977 album Terrapin Station features two dancing terrapins on the cover of the album. The terrapin has become an iconic symbol of The Grateful Dead, and a recognizable emblem among their fans.