Pigeonhole Principle

A combinatorial principle stating that if n items are placed into m containers and n > m, then at least one container must contain more than one item. Often called Dirichlet's box principle.

Combinatorial principle stating that when more discrete objects are placed into fewer containers, at least one container must contain more than one object.

The combinatorial assertion that if n+1 items are placed into n containers (pigeonholes), then at least one container contains more than one item; more generally, if more items than containers are distributed, some container receives at least the ceiling of items/containers.