Straight Ahead and Pose-To-Pose Animation are the two basic methods
used in animation.
In straight ahead animation the animator draws or sets up objects
one frame at a time in sequential order. For example, the animator
draws the first frame of the animation, and then draws the second,
and so on until the sequence is complete. In this way there is one
drawing or image per frame that the animator has setup. This approach
tends to yield a more creative and fresh look but can be difficult
to time correctly, and tweak.
Drawing or setting up key poses and then drawing or
creating inbetween images is how Pose-To-Pose animation is done. This is the
basic computer "keyframe" approach to animation, especially in 3D computer-generated animation. It is excellent for tweaking, timing, and planning out the animation ahead of time. The straight-ahead technique lends its self to creativity and strange zany and inconsistent looking work.
Stopmotion animation is entirely done using the straight-ahead technique.