Good definition of the word rhetoric

OK, so I understand what a rhetorical question is, but I need a good definition of the word rhetoric. I can't find it and I don't really understand it.

This is the dictionary's definition:

(of a question) asked in order to produce an effect or to make a statement rather than to elicit information.

A rhetorical question is a question that either doesn't have an answer or isn't meant to be answered. I.e. If a tree falls in a forest and no-one is around to hear it, does it make a noise, or How many roads must a boy walk down before he can be called a man.
They are two popular rhetorical questions.

The art of speaking or writing effectively: A. the study of principles and rules of composition formulated by critics of ancient times; B. the study of writing or speaking as a means of communication or persuasion
Basically, rhetoric means speaking or writing in a way that will be communicating with people or one person in an understandable way; an attempt to persuade a person to your view of thinking.
I've a bachelors degree in English, but it's been a Long time since I was a college student!! lol Don't think that my masters degree would be a wit of help with your question.