Similar to a guys ball/sack sweat called "Fromunda Cheese" this is found under women's boobs.
Is caused from a woman's boobs or tummy rolls being confined and overheated, thus producing Chest Gravy.
Jenny walked 2 miles on the treadmill today and went to the grocery store afterwards. She grossed out all the customers because she had so much "Chest Gravy" dripping off of her t-shirt.