The loose and wrinkled skin that drapes down the throat from the chin to the base of the neck. Most often observed in severely old people. The best examples display two unique and individual sagging sections.
Rather than submit his body to being opened via plastic surgery, Steve Jobs wore his ubiquitous black turtleneck sweaters to fend off the eventually possibility of developing neck curtains.
Hair that comes from the main section of the head, not including actual neck hair, down to cover the majority of the neck.
That medical student had a nice faux hawk with a clean neck curtain.