I have no idea what that actually is, but I have a hunch. Regardless, I'd schedule a vet visit as soon as you can.

Is that carpeting the substrate the snake has always been on? It kind of looks like maybe there was a prolapse and dragging that around got some carpet fibers ground in there.

Or maybe it's a partially impacted poop? It's hard to tell without snake in hand whether that's poop/fur or necrotic tissue with carpet fibers stuck. It definitely looks irritated though, and it's doubtful that's going to get better without some medical intervention.