Teetering (ottotto in the game's files) is an animation that is naturally activated by standing near a ledge in all installments of Super Smash Bros.. The character will automatically start teetering back and forth over the edge with a panicky expression.
The effect can only happen when a player walks toward the edge slowly. Simply landing near the edge does not count, and moving too quickly will simply cause the character to run off the edge. While teetering, a character will not walk off the edge unless the control stick is tilted past a certain amount. Because of the animation's movement, it is possible for a teetering character to dodge an attack that would have hit them were they standing up.
The player can use the teetering animation to interrupt certain moves. This technique is called a teeter cancel.