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a day approximately six months before or after the real anniversary of a person's birth. Typically celebrated by people who feel they are twice as important as everyone else or people who want to get more presents by coming up with a lame excuse.
Hey, Roshni's half-birthday is tomorrow, she's turning 21 1/2, should be get her something?

No - because it's a made up thing.
by Da Zhong October 11, 2011
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Jul 1 Word of the Day
sending two texts in a row without a reply inbetween.
Rachel: whats up?
Tessa: not to much! hbu?
Tessa: dude, i'm so bored.
Rachel: stop double texting me.
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I know you all are hot n popular and you have so many full birthdays to celebrate, so why should you bother with a half-assed attempt at your half birthday? Because it's the Best. Day. Of. The. Year. Nobody cares about your half birthday (please make no exception for mine), so do you and do it up, but don't do too much because it's your half birthday. I'm eagerly awaiting an invite to your halfway decent celebration.
Emma's half birthday is coming up on Feb 1. At half past one, she's taking her friends hiking. At half past six, they're making half-assed pizzas. They'll finish off the festivities by getting half baked and playing half a game of something or other.
by EvPlatt January 27, 2020
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You're birthday but half the way inbetween your birthday from the previous and next year (:
by yapdizap April 04, 2009
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