It means something different depending on age group:

0-3: Too young to understand
4-9: Best day of your life
10-14: Day you're treated better than usual
15-19: Day opposite sex is more likely to put out
20-death: Day to celebrate a year closer to death*

*Exceptions is with your 21st Birthday due to it being the legal age of adult and you are now considered old enough to consume alcohol legally and some age in your mid-sixties due to being old enough to retire.
Birthday reactions:

Young child: YES!!!!! I'm now a year older!!!!
Pre-teen: Yes! Closer to a teenager
Teen: Hopefully a (member of opposite sex) will do me tonight
Adult (Normal): Hooray I'm a year closer to the grave.
Adult (21): TIME TO GET DRUNK!!!!!!
Adult (60s): Finally, I can retire
by Gaaraofthedamned July 12, 2011

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In technical terms, the day and month that you entered this world, by exiting your mothers womb.

In Facebook terms, the day when people that you don't know decide to write a somewhat personal message on your wall, congratulating you on this occasion
Charlie: Happy Birthday Ashley! hope you have alot of fun tonight! maybe we can see each other later

Ashley: Charlie, who the hell are you?

Charlie: We met at Emily's party three years ago! remember? I introduced myself, you said go away I have a boyfriend, and then sprayed pepper spray on me? I sent the whole night crying in the bathroom!

Ashley: oh yeah sorry about that. By the way I dont have a boyfriend anymore. You wanna get together later?
by jrfredrick10 July 31, 2012

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On his birthday, Charlie consumed twice his weight in beer.
by asdfasdfasdfasdfg January 05, 2012

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A word that rappers love to use.
...We gon' party like it's yo birthday....
by hublah12354 August 04, 2011

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The one day a year when your Facebook notifications rocket and your wall gets filled with other people's posts.
Ted Jones
Happy Birthday!
Like · See friendship · 2 hours ago
by SerJ1000 October 26, 2011

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A day in which the only person having fun is the person being celebrated.
birthday
by googlemegg July 10, 2008

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Being thrown out of the place you live
"Saw Todd on the street the other day with all his stuff in a pile"

"Yeah, it was his birthday yesterday.
by guestguestguest4 November 21, 2012

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The Urban Dictionary T-Shirt

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The Urban Dictionary T-Shirt

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