Sagging muscle edges. This usually refers to the central edges of the platysma muscles, very thin muscles in the neck just below the skin surface that basically have no function. You can tense these by showing your bottom front teeth. With aging, the muscles stretch and relax and their inner borders become prominent, appearing as two parallel lines at the front of the neck. There are many operative approaches to this.
Not related. Turkey neck ins a reference to lax and hanging skin under the jaw area, usually associated with aging and loss of elasticity or significant weight loss. These occur in all races, not just caucasian.