This glitch requires a 45 degree ramp, which is preferably a fall-through platform placed somewhere above the ground. Using Sonic's Spin Dash or Jigglypuff's Rollout, the character shoots off the end of the ramp, but continues to fly through the air in a straight path, unaffected by gravity. They will not stop until the player cancels the move with an attack, is themselves attacked, the attack is completed or flies behind a blast line.
Additionally, when used by Sonic, if he hits or is hit by anything, he will teleport upward a huge distance, while the Spin Dash continues uninterrupted.
Spin glitch 2
The Spin glitch 2 is another glitch that can be performed by Sonic. To perform this glitch, Sonic uses the Spin Dash or Spin Charge (preferably a charged Spin Charge) to go up a slope/ramp (optional, easier this way). At the very end of the animation, which the player has to make sure is at the top of the slope/ramp, the player presses the direction that is opposite Sonic's direction, which will be down the ramp. If performed incorrectly, Sonic will slide a short distance. If performed correctly, he will quickly slide a large distance, sometimes falling of an edge to a Self-destruct. To give an idea as to how potent this glitch can be if mastered, it is possible to go from the farthest left spot on Temple to the base of the stage in less than one second.
A video of Sonic using the Spin Glitch on Pictochat: