Question
The title should say it all, but to add to it: she hasn't been seen by a vet for a few years, but last time she was there the vet thought she was in good health and just a, "larger" cat and not fat. Since then she appears to have slowly gotten what appears to be either a very saggy belly or very saggy rear-breasts.
She is spayed and has been since early youth. She quite active for an indoor cat and has a healthy eating habit (e.g. She grazes throughout the day and doesn't overeat). She has no signs of any kind of illness what-so-ever, including any behavioral or activity changes. She can jump quite high despite the extra baggage in the back and is very agile.
Specifically, the baggage is right where he furthermost rear nipples are, which is large why I am having a hard time determining which it is. Also, her other breasts are totally normal.
Answer
Per the Wikihow article that trond hanson posted, #5:
Do not be overly concerned about a saggy belly. Many cats have a saggy bit of flesh that hangs down between their back legs. If your cat is otherwise bony, this small pouch of skin is unlikely to be an indication of a weight problem. This skin flap is referred to as the "primordial pouch" and its purpose is to protect the stomach during fights with other cats. Cats often kick with their back legs when angry, and this flap of skin protects your cat from such attacks. Many cats will develop a primordial pouch at some point in their lives and it is not necessarily an indicator of feline obesity.
Since my cat passes the other tests, this sounds like the answer since it is exactly what she has.
Answered By - Nick Betcher