According to Aristotle, rhetoric is "the faculty of observing in a given case the available means of persuasion." In contemporary terms, "rhetoric" is the social science that focuses on how to use language to create understanding and to change attitudes or behaviors.
The earliest known works on rhetoric predate Aristotle, and rhetoric was an important part of a young Greek male's education to be a civic leader. Aristotle's theories were widely adopted and refined by rhetoricians of the Roman Empire, and later by Christian scholars. For over 1,000 years -- from about 600 A.D. to about 1800 -- rhetoric was one of the three liberal arts studied by every educated person. (The others were grammar and dialectic.)
Around 1900, "rhetoric" became primarily the study of how to write effectively, while "speech" dominated college curricula as the study of effective persuasion. Today, these divisions are much less clear, but "rhetoric" is often distinguished from "communication studies" by a greater emphasis on criticism and practice, versus empirical or laboratory studies.
In current usage, "rhetoric" has four connotations:
1. "Empty rhetoric." The popular use of the term to mean using words to confuse, bully, or obscure the issue.
2. Writing skills. Many departments of rhetoric focus on writing, especially technical writing.
3. Rhetorical theory. There is also a body of theory on how rhetoric works, some of it overlapping with literary theory.
4. Rhetorical criticism. The application of rhetorical theory in order to understand why a speech (or ad, or song, or whatever) was or was not persuasive.