A G6 is a jet. A plane. When she says, "I feel so FLY like a G6", she says that because a G6 is a plane and planes fly.

Another, somewhat fun, answer to the question is Hot For Music's analysis of the whole song: http://www.youtube.com/watch?v=sQah2-sO-_Q

if you're referring to "Like a G6" song, you may try this link. http://en.wikipedia.org/wiki/Like_a_G6 :)