Equipment
Fin
A blade fixed under the tail of the board that stabilizes its trajectory and provides drive and hold through turns.
Fins sit underneath the board to stabilize its tracking and give the rider traction through carves. Surf-style boards usually run two or more larger fins for stability and drive, which makes them carve powerfully but resist spinning. Skim-style boards run little or no fin so the board pivots freely for spins, shuv-its, and slides.
Fin count and size are thus the single biggest factor distinguishing how a board rides: more fin equals more hold and carve, less fin equals more looseness and freestyle ability. Many fins are removable so a rider can tune the setup.