an MC flows with lyrics right off the top of his or her head. It is inpromptu and spontaneous
and only the most creative rhymers can do it well. It is also
a kind of competition
between MC's because you have to be good to bust a good freestyle. It helps to keep MCs on their toes too, because it is like practice.
"We gonna do a little freestyle for y'all, and it go like this" -- Schoolly D (Cuttin' and scratchin').