A: Well, being that you are a woman, I am going to use your extensive laundry experience to illustrate this :)). You know what towels look like when you pull them out of the washer (before you put them in the dryer), the whole towel is still there but it looks so much smaller and all clamped up? Well, that is your clamped fin betta.
Or let us do this. I want you to stand up, with feet apart and raise your arms in a V shape and stretch them out as far as they can. This is your healthy betta with fins that are open and spread out. Now I want you to put your feet together and bring your arms down along your body. This is your clamped fin betta. The fins are still there, they just are not open. They are in a closed position, so the betta looks as small as possible.
OK, so you are like: "Laundry, Gymnastics, this is all fine and dandy but I still can't visualize it.". Very well then, let us use the old "a picture is worth a thousand gyrations" moto :)).
So here is two photos of a female, which will clearly show the clamped fin look. Please take a moment to click on each photo to see a bigger version of it.:
Bettas will go into a clamped fin position for a couple of reasons: