I am not a vet or anything like that, but it could possibliy be a skin tag or a lipoma. A lipoma is most common in middle-age dog. Lipoma are usually under the skin, but they can be locally invasive, meaning they are meshed with muscle or connerctive tissue.
You might want to check with your vet just to be safe.
I hope it is nothing to serious!
"A house is not a home without a pet"