Chinstrap beard
A thin line of beard that follows the jaw from ear to ear like a helmet strap.
Also: chinstrap
A chinstrap is a narrow band of beard along the jawline and under the chin, usually with the moustache shaved. It outlines and defines the jaw, so barbers sometimes suggest it for round faces. It needs frequent trimming with a steady edge, top and bottom. A wider version that also leaves the upper lip bare is called a chin curtain.