Ptosis is drooping or sagging of any tissue. Pronounced as in "toe-sis". If you say "puh-toe-sis", you're giving yourself away as a newbie.
Most commonly, we refer to ptosis in cases of Breast Ptosis, Brow Ptosis, and Eyelid ptosis. It can be used to describe any tissue that is displaced lower than its usual position, for example, "ptosis of the cheeks". Your own doctor may not say the word ptosis to your face, as he is afraid you will not understand. On the other hand, you may use the word yourself to describe your own condition, and he will rightly be impressed that you are an informed patient.