An "Astyn" is a female who farts incredibly loud and smelly. An Astyn will make you want to throw your body out of the car when she lets one loose unexpectedly. Usually, an Astyn chooses to keep the fart silent in hope of having people around her freak out all of a sudden gasping for air.
I was in the library next to the bathrooms today and heard an Astyn in the bathroom let one loose. As soon as the girl walked out I started gagging.