Definitions by Da Zhong

Half-birthday

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.

Half-birthday by Da Zhong October 11, 2011