An overweight female who remarkably resembles a the endangered freshwater mammal of the same name (also known as a "manatee" or "sea-cow.") Although the term can be loosely applied at any given time, it is most appropriately used when viewing overweight females at the pool, beach, etc...
Call PETA, somebody's keeping a Dugong in their pool.
A Dugong is a girl whom is absolutely hideous, so ugly that you vomit in your own mouth every time you see one, but one that you can guarantee sex from. She is so desperate that she will take what ever is coming her way!