The nasty hair that grows from the back hair line down your neck.

the first example wants to make me throw up.

The accumulation of breast milk, formula, perspiration, shed skin cells, spit up, and saliva that gets caught in the neck creases of an infant, and creates a powerful odor (like stinky cheese). May precede or accompany intertrigo or a yeast infection.

the lingering odour of a fat person's neck, especially at the top of the neck. usually a horridly rank mix of dairy products and unusually high sodium content and the inability to scrub that unreachable area of the neck that plagues the obese.