An overbite is about how the front teeth meet. In a usual bite, the upper front teeth sit a little over the lower ones. When that overlap is too deep — the top teeth cover the bottom ones more than they should — dentists call it an overbite. It is a body word, used in clinics and in ordinary talk about teeth. A small overbite is very common and not always a problem; a large one can make chewing or closing the mouth harder, and a dentist may want to treat it. The opposite picture, when the lower teeth sit too far forward, is an underbite. Though actually, learners (and a lot of adults) mix it up with teeth that stick out toward the lip. Sticking out is a different line. Overbite is more “how far down they hang over”, not only whether they jut forward.