van der Waerden's theorem

Etymology
Named after the Dutch mathematician B. L. van der Waerden.

Proper noun

 * 1)  In Ramsey theory, a theorem stating that, for any given positive integers r and k, there is some number N such that if the integers {1, 2, ..., N} are colored, each with one of r different colors, then there are at least k integers in arithmetic progression whose elements are of the same color.