n. Used to describe a "friend" who follows another friend to various parties, get-togethers, or shindigs without ever being invited himself.
"Oh, hey Jack. I see you brought a special feature with you."
The rule that applies to lost or fallen objects, typically food, that hits the floor. The rule applies to general areas, and does not apply to anything in a bathroom. Using this rule makes it OK to pick up said object in under 5 seconds, under the presumption that no germs attached themselves in such a short period of time.
If your gum just dropped on the floor, pick it up and say "5 Second Rule", then place it back in your mouth.