look up any word, like pussy:
A combination of Birthday and YAY!, typically to indicate excitement about a birthday; a portmanteau of "Birthday" and "YAY".

See "FriYAY" for reference.
Karen - "Woo hoo! It's my BirthYAY weekend! We're going out!"

Ann Marie - "Weekend?! It's my BirthYAY Month! We're going out repeatedly!"
by AMarie0908 May 27, 2011