Neckline
How the hair is finished at the nape: squared off in a block, rounded, or tapered to the skin.
Also: block neckline, tapered neckline
The neckline is the finish at the back of a short haircut. A blocked neckline is cut straight across in a sharp line. A rounded one curves at the corners. A tapered neckline grows gradually shorter until it meets the skin, so it still looks neat as it grows out. Barbers usually ask which one a client prefers. The choice also depends on how the hair grows at the nape and where the natural hairline sits.