Tic Tac
Tic Tacs are used as a method of propulsion for freestyle skaters. It is also used for turning since freestyle trucks are using too tight to carve a turn. The basic concept goes like this; The skater pushes down on the tail, to raise the front wheels off the ground, while simultaneously moving the nose to the left or right 45 degrees or so to create some momentum, then set the front wheels down. Then do the same in the opposite direction. When doing this smoothing and consistently, you can propel yourself forward without putting your feet on the ground.
This creates a "snake" like slithering effect. To turn, the rider will not alternate to the opposite direction the rider moved them in the last time. The Tic Tac was crucial in the heyday of Freestyle skateboarding when points were deducted from a rider in a contest run if the rider's feet ever touched the floor. The rider would not be allowed to pedal and needed to Tic Tac to regain speed