Final answer:
A gomphosis is a type of fibrous joint that functions as a peg-in-socket to anchor the root of a tooth into its bony socket in the jaw, connected by the periodontal ligament.
Step-by-step explanation:
A fibrous joint that is a peg-in-socket is known as a gomphosis. This specialized fibrous joint anchors the root of a tooth into its bony socket within the upper jaw or lower jaw of the skull. The connection in a gomphosis is made by numerous short bands of dense connective tissue, known as the periodontal ligament. Due to the immobility of a gomphosis, it is functionally classified as a synarthrosis, which is a type of joint that permits little or no mobility.