Persuasion defines ones charisma, or ability to influence others by any means.

Having high Persuasion means you likely wouldn't need to use any EGO or ID Skills to elicit a specific response from someone in dialogue. Could be used for bartering a better deal out of a sale, or convincing someone to make a certain decision. It could even be as significant preventing a fight or ending a lethal deicision. It can be both a very powerful tool for the ill-intentioned AND the manipulative.