Snapping turtles are generally not considered terrapins, however there is room for debate.

There is some confusion about what a terrapin actually is, but a commonly accepted meaning of the term is that terrapins are merely turtles which live is brackish water, as opposed to turtles (which live in fresh water) and tortoises (which live in salt water). You could think of a terrapin as a sort of “in-between” distinction separating turtles and tortoises.

Since snapping turtles live in only fresh water, they are not typically thought of as being terrapins.