What exactly IS a Turtle?

Everyone knows turtles - those interesting reptiles with shells on their backs, no teeth, and a reputation for slow speed. But you also hear about tortoises and sometimes terrapins, and looking at pictures of the three animals may have you thinking "What's the difference?". It depends partially on where you live as well as being a matter of taste. Here's a quick guide on how to name your chelonians ("chelonian" is the Latin name for the turtle family).

First, there are the ocean-living chelonians. These animals are generally quite large. They can move on land - just barely - but they are very much aquatic creatures. These animals are often called "turtles" or "sea turtles".

Next are the amphibious chelonians. Frequently kept as pets, these creatures live in freshwater. While generally called "turtles", people living in the UK may call them "terrapins", and some people in the United States will use the term "slider".

The fearsome-looking snapping turtle is always called a turtle, and doesn't fall into the same group as the other freshwater turtles.

 This species is called the diamondback terrapin. This is the only turtle regularly called a terrapin by people outside the UK.

Finally, the family of land-living chelonians is referred to as "tortoises" or "box turtles". The UK generally prefers "tortoise", while most of the USA prefers "box turtle".

In short, if you want to tell the animals apart without just calling them all turtles, use "tortoise" if it has legs and "turtle" if it has flippers or webbed feet.

Here's my personal preferences on this important issue:
Ocean - Turtle
Freshwater - Turtle (exceptions: the red-eared slider and the diamondback terrapin)
Land - Tortoise