The jaw or chin—the bone and flesh at the lower part of the face.
転んで顎を強く打った。
I fell and hit my jaw hard.
彼は顎に傷がある。
He has a scar on his chin.
あごを上げて顔を見せてください。
Raise your chin and show your face, please.
The barb of a fishhook (the small projection that prevents the hook from slipping out); a specialized term used in fishing contexts.
釣り針の顎が折れていたため、魚が外れてしまった。
Because the barb on the hook was broken, the fish came off.