It doesn't really need to be defined because it's not a very difficult concept to grasp.
1. Play your character from your character's point of view, considering only what your character has experienced or has knowledge of. Do not allow knowledge gained with another one of your characters or from OOC sources to affect the decisions made by the character.
2. Play it safe and avoid situations where it may appear you are violating the first point. Two characters working together in the same location, despite the fact that said interaction may be perfectly IC behavior for the characters in question, can look potentially suspicious.
That's all that really needs to be said. Why do we have to spell this out so legalistically? Is it really necessary? Do we have to find every friggin' loophole and push it to it's limits? Can't we just play the game and operate on common sense? Apparently not. I guess
Common sense truly is the
rarest commodity in the world!!!

I must be like the richest guy in the world.
Please stop the bitching about this. It's incredibly annoying! It's a friggin' game, not law school!

"Y-O-U! It's just two extra letters! Come on, people! This is the internet, not a barn!" --Kid President