Homie typically refers to home boy or usually some one we know really well. The term is generally used to greet you friends on how they have been doing.
a: Been long bro! Sup Homie?
b: Nothing muchbrother! Sup with you?
"Sup" from contraction of "What is up?". "Man" used in brotherly sense, as in "homie".
Term used in same situations as "What's up?" but shorter and cooler.