five-second rule

Short definition from Wiktionary

Noun

1. 1
   Any rule that allows or prohibits certain behavior for five seconds after some event, especially: The belief that food dropped on the ground is still hygienic to eat provided it is picked up within five seconds of touching the ground.
2. 2
   Any rule that allows or prohibits certain behavior for five seconds after some event, especially: A rule that a closely-guarded player cannot hold the ball for more than five seconds without dribbling, passing, rolling, or shooting the ball.
3. 3
   Any rule that allows or prohibits certain behavior for five seconds after some event, especially: A rule that a player who throws in the ball from out of bounds must get rid of it in less than five seconds.