What is neck? What is neck? Anatomy The part of the body joining the head to the shoulders or trunk. A narrow or constricted area of a bodily structure, as of a bone, that joins its parts; a cervix. The part of a tooth between the crown and root.The part of a garment around or near the neck.A relatively narrow elongation, projection, or connecting part: a neck of land; the neck of a flask. Music The narrow part along which the strings of an instrument extend to the pegs.Printing See beard.Geology Solidified lava filling the vent of an extinct volcano.The siphon of a bivalve mollusk, such as a clam.A narrow margin: won by a neck.