1. The Action of Directing; pointing (Something) towards.
2. The path or course of a given movement, or moving body; an indication of the point which the object is moving.
It's something I believe is in a lot of old cartoons but wasn't really talked about clearly mainly cos it's hard to explain but I'll try my best.
It's the logical way to apply most of the principles of animation. It's about thinking (Not feeling) through the intension of the drawing, focusing on the result and not the formula (The Principles).
Now when I say "Direction" I don't mean the character should always be doing something (A character doing nothing can be a point of focus to draw) but whatever it does (or doesn't do) should be the natural number one focus (In my opinion).
Now please don't confuse what I mean by "Direction" with any of the other principles like "Line of Action", "Exaggeration" etc etc...I believe it works into all of them, it supports and selectively chooses what principles to use based on situation. As Popeye says "Can't make a cartoon without an idea" which applies to many factors in an animation.
Look at this pose of Tom, the direction of the pose is he is punching another cat by leaning forward and tension up his shoulders and the another cat is folding up as the line of action and silhouettes are clearly telling us.
If someone was going to try and copy this, they would purely copy the line of action then the pose, the construction and finally the details. I think the process of coping leaves out the "Direction" that is using in creating because you've got the answer right in your face, it leaves the reason to think about where your heading in your own drawing. The intension behind it which I think makes it hard to understand "Direction" when you make your own drawings.
These are some of the things that help line of action, silhouettes, exaggeration and even appeal work well because the artist (Preston Blair) knew where he was going with his drawing, the direction of where he was going.
"Focus on the Result...Not the Formula"