The terms 'turtle,' 'tortoise,' and 'terrapin' are often used interchangeably, and depending on which country you are in, may describe a completely different type of 'turtle.' But before you get too concerned about the common names, let us take a step back and identify them as belonging to one common order, the Chelonia. If it has a shell and is a reptile, then it is going to fall into the order Chelonia, which includes 244 different species.
For most Americans, the term 'turtle' describes the Chelonians that are aquatic or semi-aquatic. The term 'tortoise' describes a Chelonian that lives primarily on land. 'Terrapin' can describe some freshwater or saltwater turtles, but is not often used.
If you were in Australia, you might call all of the turtles 'tortoises,' and in Britain, a 'turtle' would mean a saltwater species and a 'terrapin' would be a freshwater species. Are you confused yet? Good, so am I. So for the purpose of this article, let us call the species that live on land, tortoises and the species that are aquatic or partially aquatic, turtles. We will forget about the term terrapin for now.
While there can be a lot of differences between individual species, for the ease of comparison, I am going to go out on a limb and make a couple of general assumptions about the difference between turtles and tortoises. In general, tortoises live on land and eat a primarily vegetarian diet, and turtles live in or near the water and eat a meat-based diet or a combination of meat and vegetation. To take this one step further, turtles are often broken down into aquatic and semi-aquatic species. The aquatic species spend the majority of their lives in or near the water and eat a diet that is mostly meat based. Semi-aquatic turtles spend a greater period of time on land, but periodically enter the water. Semi-aquatic turtles tend to eat both plants and animals. An example of a semi-aquatic turtle is the well known American Box Turtle. While there are several subspecies differences, this turtle tends to spend most of its time on land, but enters very shallow water several times a week to defecate. The young turtles are primarily meat eaters, but as they get older, they eat a primarily vegetarian diet.
If you interested in obtaining a Chelonian, these differences in environment and diet are very important considerations in determining which type of animal would be best for you. In addition to these factors, there are other important issues you should consider before obtaining a turtle. Read "Turtles as Pets" to learn more.