Flow encompasses a lot of things...an MCs ability to flow with or ride the beat, his delivery on the beat...meaning how well he sounds, how he adapts his voice to the tone of the beat/matching the mood, how well he brings forth his words, how well he makes u feel what hes saying, how he makes shit sink in. Charisma/Confidence play in2 this, how well u know ur shit plays in2 this, breathe control plays in2 this, and ur skills as a rapper definately play in2 it. Examples of good flow that come 2 mind are: Tech N9ne, Brotha Lynch Hung, TI, BlackStar, Common, Bad Azz, etc...