I would call it an all purpose saddle, because it is. Describe it exactly as you described it here. Give brand name and give its official size. Then measure it yourself to be sure that is accurate. If it isn't, say its a 17.5 inch saddle but I measured it as a definite 18". Give the length of the flaps, as well, because those are so much a part of this saddle, it will influence what rider it will fit. Include a picture. Most people don't consider a used saddle they can't see.
Airborne? Oh. Yes, he can take a joke. Once. After that, the joke's on you.
I love mine, you'll probably get a good price for it too very comfy!!
If so, you describe it as it is, I think a fair number of people know about them - I would call it an a/p if you have to pick a category
Only the County Drespri comes to mind-- flap "swings" into different positions. Is that what you meant?
Otherwise and in general: Yes, describe it as an AP saddle. If you give the brand and name, the right buyers (who already know the saddle) will show up. Many sellers ad text from the manufacturer's website. That can help if you want to fine-tune your description or also decide whether to describe this as an eventing saddle, or the shape of it's seat.