What is Delivery? What is Flow?
To me, they are the same. In short, its about how smooth and fluid your words come out to the rhythm of the beat. An emcee with great flow doesn't have problems with trying to squeeze too many words into a rhyme, or stanza, no problems with ever being off beat. The ability to maintain breath control is also very key. When I hear a rapper run out of breath too early or it seems unnatural, it leaves a slight feeling of unprofessionalism (new word for the day), or better yet, it reeks of an amateur. Its the subtle attention to detail that separates the great from the good.
Great examples of emcees with supreme delivery and flow would include artists such as Twista- who can flip words at a slow or rapid fire pace and never lose his continuity. Eminem, Ludacris and Drake are a few others who are very skilled at keeping a natural rhyme pace. Study these emcees.
Rap 101 (According to Mau)