If asked to name a reptile that has a shell on its back, you’d probably say, “a turtle.” But that description fits tortoises too. What’s the difference between turtles and tortoises, anyway?

Tortoises live on land, in dry environments. Some of them, like Galapagos giant tortoises, are huge and weigh  over 900 pounds—more than a small horse. Others, like the speckled tortoise, are tiny and weigh just a few ounces.

All tortoises are turtles, but not all turtles are tortoises. Tortoises live only on dry land, but many turtles live in the water. Some, like loggerhead turtles, live in the ocean, while others, like painted turtles, live in ponds. Some turtles live almost their entire lives in water, but some switch between land and water.

If you’re a reptile fan, you might have heard the word “terrapin” used to describe some of these creatures. What’s a terrapin? It’s not a hard and fast scientific descriptor—it’s a word commonly used for some small freshwater turtles. For instance, the turtle in this picture, a red-eared slider, is also known as the red-eared terrapin. Red-eared terrapins are common throughout the US!

Photo by Greg Hume