Straight Ahead Action in hand drawn animation is when the animator starts at the first drawing in a scene and then draws all of the subsequent frames until he reaches the end of the scene. This creates very spontaneous and zany looking animation and is used for wild, scrambling action.
Pose-to-Pose Action is when the animator carefully plans out the animation, draws a sequence of poses, i.e., the initial, some in-between, and the final poses and then draws all the in-between frames (or another artist or the computer draws the inbetween frames). This is used when the scene requires more thought and the poses and timing are important.
This is similar to keyframing with computer graphics but it must be modified slightly since the inbetweens may be too unpredictable. For example, objects or parts of objects may intersect one another. Computer keyframing can take advantage of the hierarchical model structure of a complex object. Different parts of the hierarchy can be transformed at different keyframes. For example, in a jump, translation keyframes can be set for the entire model in the X and Z directions. Then other rotation or translation keyframes can be set for portions of the model, e.g., the legs and arms.