It's just a flap of skin. Basho says it makes him look gorgeous!

Perhaps that's just another trait some male cats share with
some male humans?

Princess (Siamese RB 16)had drooping flaps when she first adopted me.
However, after she was a house cat for a few years the flaps disappeared.
I remember reading something about it a long time ago but can't remember
what I read but I think it is a protective device in the wild.  As I
recall, there was a name for the flaps.   MLB

Both of mine have flaps.  Dot, weighing about 10 lbs, has a droopy
flap covered in long white fur that contrasts with her black body and
thighs, and it looks very funny from behind, especially as she's
walking.  I give it boops when she begs to have her tummy kissed.

Buster, who's grown to about 12 lbs, has a full, squishy flap, and
when he's upside-down in my lap, I love to knead and massage its
squishiness. :)

I'd asked my vet about that, on one of my boys.  She said that she
always called it a 'dewlap', and that it was to protect the innards
during a cat fight (the bunny kicks).  The dewlap could be shredded,
but nothing internal would be wounded, so they were more likely to
survive the fight.

Made sense to me, and I always presumed that dewlap meant that it was
likely to "lap" at the dew on the grass (okay, that sounds lamer than
I intend, but you know what I mean).

Smokie Darling (Annie)

My (RB) White Princess, Blizzard, had pronounced flaps even when she was
only a few years old.

I recall a friend asking if she was pregnant! (No, she was spayed...).

It was funny to watch her run, as the flaps would go from side to side.

They were very, very soft, and Blizzard loved to get tummy rubs.

Kenzie has smaller ones. She's not real big on tummy rubs, but I like to
give them, because the white fur on her tummy is soo soft.

~~~~~~~~~~~~
"Life without cats would be only marginally worth living."
-TC, and the unmercifully, relentlessly, sweet calico kitty, Kenzie.

How you behave towards cats here below determines your status in Heaven.
- Robert Heinlein

Life is very difficult. Once you understand that, life becomes easier.
-Buddha

Hehe we have a cat at the vet clinic named Rosie.  She's sort of a
long haired tabby

Well a few times a year one of the groomers will give her a lion cut.

she's at least ten, and has that customary pouch on her belly.

but the first time I saw her shaved I practically fell onto the floor
laughing.

The pouch was drooping so much it almost touched the floor.  In fact
it FOLDED inward and if you looked at her straight on it looked like
she had an udder.

If you think THAT image is funny, you ought to see her when she runs.
The 'udder' will SWAY from side to side.  hehehe

Kristi