opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food; structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals
For the movie about a shark, see Jaws (movie).
The left side of a human jaw

The jaw is the bone in the mouth that, in humans, lets the mouth move up and down in order to chew. It is joined onto to the skull.

However, in insects, the jaw may open left and right instead.