This is the wet substance that occurs in your ass crack. This is much like the sweat on the rest of your body but with a distinct scent and a thicker solution. You can tell you have swaas if you scratch your lower back and feel a gewwy slim at the peak of the crack, or it smells like you have takein a dookie in your pants.
"It was so hot outside today that I had swaass, like a five dollar French horror!"
Having a very sweaty crack on a humid day
"it was so hot my ass cheeks were slipping! I had mad swaass"