Wiktionary
birthday attack
n. A method of code decryption which exploits the so-called birthday paradox.
Wikipedia
Birthday attack
A birthday attack is a type of cryptographic attack that exploits the mathematics behind the birthday problem in probability theory. This attack can be used to abuse communication between two or more parties. The attack depends on the higher likelihood of collisions found between random attack attempts and a fixed degree of permutations ( pigeonholes).