From Rap Dictionary
- Kilo. Specifically, of cocaine. "A bird in the hand" -- Ice Cube (A bird in the hand ).
- English slang for 'girl'. "Around here we say 'birds', not bitches" -- The Streets (Let's Push Things Forward) 
- A gun. (Desert Eagle, Hawk, etc.)
- A jail sentence
- The middle finger, especially when saying "flipping the bird."
- A bullet. "when mel-man got his time he shot birds at the judge" -- Young Jeezy (Soul Survivor)
Stupid, ill-mannered, small-minded. "....Bird ass niggas, I don't mean to ruffle y'all..."--Jay-Z (Never Change)