Both turtles and tortoises are reptiles that belong to the order Testudines, which also includes the terrapins. Tortoises are assigned to a subclass of Testudines, the family Testudinidae.
Turtles and tortoises have slight physical differences in their limbs, but their chief distinction is habitat. A tortoise spends most of its time on land, while a turtle spends significant time in the water and emerges onto land chiefly for the purpose of laying eggs. A way to keep this straight might be to remember that it was the tortoise, not the turtle, who ran against the hare—in a race held on land.
In addition, tortoises are generally herbivorous, while non-tortoise turtles will include insects and snails in their diet.