1) Certain garment edge 2) Collar 3) Décolletage 4) It may be plunging 5) Neck 6) Open neck 7) Polo neck 8) Roll neck 9) Turtle neck 1) Decolletage 2) Fret 3) Lapel 4) Lasso 5) Neck 6) Vee 
The neckline is the top edge of a garment that surrounds the neck, especially from the front view. Neckline also refers to the overall line between all the layers of clothing and the neck and shoulders of a person, ignoring the unseen undergarments. For each garment worn above the waist, the neckline is primarily a style line and may be a boundary...
[n] - the line formed by the edge of a garment around the neck
noun the line formed by the edge of a garment around the neck
the opening at the neck of a garment, esp. of a woman's garment, with reference to its shape or its position on the body: a V-neckline; a high neckline.