This word gets tossed around a lot. We'll give you the real lowdown.
Rhetoric is the art of argument; that is, persuading someone to see your point of view.
Ancient scholarly dudes like Aristotle had lots to say about how to do just that, and many of these rhetorical principles from the classical period remain today. When we try to persuade people, we use rhetorical devices like rhetorical questions, parallelism, and hyperbole (just to name a few).
In modern times, the word rhetoric can be used as an insult to suggest that an argument or a political position is all sound and fury signifying nothing. If someone ever accuses you of using empty rhetoric, well, suffice it to say, that's not a compliment. Unless you're trying to be a politician.