The terms turtle and terrapin can easily be confused as both of these animals belong to the Order Chelonia and are Reptiles. In the United States, any animal from the Order Chelonia has been termed a Turtle which is not entirely correct, and there are differences between the two groups of animals.
References
- https://books.google.com/books?hl=en&lr=&id=aC5zDwAAQBAJ&oi=fnd&pg=PP1&dq=turtles&ots=7-BXrQkYnr&sig=IroqkzAjvUmC_-WasLTbHyJyONM
- https://books.google.com/books?hl=en&lr=&id=HA9bDwAAQBAJ&oi=fnd&pg=PT9&dq=terrapins&ots=OaJq72Tc5w&sig=6FxmY0ChJb_zMZz6jmuvH7TWFqw