Diplomat governs the minor skills: Appraise, Bluff, Intimidate, Persuade. Appraise, Bluff, Intimidate, Persuade.
Once per day, per point spent in diplomat, you can assess a social situation to get guidance from the GM on the best way to proceed. Should you try to lie, scare them or persuade them? Or is talking not even going to be an option here? The level of detail is to the GM's discretion based on the situation at hand.