Here are the big ones I can think of:
The noun: In rules for actions, the first object that the action applies to.
The second noun: In rules for actions, the second object that the action applies to.
The topic understood: In rules for actions that take free-form text instead of object names, the text that was input. (e.g., If you type “SET DIAL TO FORBO”, the topic understood would be “FORBO”.)
The person asked: In persuasion rules and rules for actions, the person who is being asked to perform an action, or the person who is carrying it out.
The actor: In rules for actions, the person who is carrying out an action. (I’m not sure how much this differs from “the person asked” in most cases.") [UPDATE: Right, there’s some potential weirdness with “the actor.”]
The location: The room enclosing the player.
Anyone got some more? I may not have these all quite right, especially “the person asked.”