de Bruijn-Erdős theorem

Etymology
Named after the mathematicians Nicolaas Govert de Bruijn and Paul Erdős.

Proper noun

 * 1)  A theorem stating that, when all finite subgraphs of an infinite graph can be colored using c colors, the same is true for the parent graph.
 * 2)  A theorem that states a lower bound on the number of lines determined by n points in a projective plane.