Rhetoric is a type of speaking or writing used to persuade an audience of the validity or truth in the statement. The use of rhetoric typically masks the real truth under discussion or leads persons astray or off the track of the "real" argument under discussion. Rhetoric typically obfuscates the issue.
Rhetoric was written by Aristotle in Ancient Greece around 335 and 322 B.C. in Athens. Rhetoric discusses methods of persuasion, logical and ethical proofs, and the style and arrangement of rhetorical arguments. (http://www.enotes.com/classical-medieval-criticism/rhetoric) Socrates studied under Aristole and developed his own style of rhetoric.
Socrates: The fact is, as we said at the beginning of our discussion, that the aspiring speaker needs no knowledge of the truth about what is right or good... In courts of justice no attention is paid whatever to the truth about such topics; all that matters is plausibility... There are even some occasions when both prosecution and defence should positively suppress the facts in favor of probability, if the facts are improbable. Never mind the truth -- pursue probability through thick and thin in every kind of speech; the whole secret of the art of speaking lies in consistent adherence to this principle.
Phaedrus: That is what those who claim to be professional teachers of rhetoric actually say, Socrates.
--Plato, Phaedrus 272
There are a number of rhetorical devices used in modern speaking and writing. Below in the links section you will find links to two lists of rhetorical devices, definitions and examples.