half birthday

Noun

 * 1) The day halfway in between two consecutive birthdays.
 * 2) * 2003, Meg Cox, The Book of New Family Traditions, page 263:
 * You can sing "Happy Half Birthday to You!" or you could try only singing every other word.
 * 1) * 2004, Ginnie Mesibov, Outer Strength, Inner Strength, page 39:
 * The fete was Mary Beth's half-birthday.
 * 1) * 2009, Philip Done, Close Encounters of the Third-Grade Kind: Thoughts on Teacherhood:
 * “Your halfbirthday?” I pointed to the plate.