Introduction.
Straight ahead.
Straight ahead animation is where an animator will draw each frame in chronological order, with one following another. Rotoscoping and flip books are examples of straight ahead animation.
Pose to pose.
Pose to pose animation is where the keyframes are drawn first, and then in between frames are added in later to build up the animation from an animatic. Key frames are the frames that show the full pose of a character or the most basic moments in an action. Breakdown frames are the frames that show the transformation from one pose to another. In-between frames are frames that serve to smooth out the animation by going in between the key frames and breakdowns.