Frame by Frame is an animation style that is very hard and very time consuming. Is basic terms, its drawing a picture, keyframing it, creating another keyframe and redrawing the picture. Wallace and Gromit are done frame by frame for an example. However, this is very hard to do as the redrawn picture should be exactly alike to the frame before with minor movements, or else the result is very fast or choppy. I wouldn't suggest doing it, but sometimes flash's shape tweens are a bitch and they force you to frame by frame.