A fork of Rural Dictionary
A mountain bike feature leading into a jump with a lip at a 45 degree angle. Leads to a sideways jump and requires the rider to twist his bike mid-air to prepare for the landing. The feature sticks out of the ground like the fin of a shark that's crossing the trail.
Rider 1: Dude, see me send the shark fin??
Rider 2: Totally. That was sick, bro!