The study of rhetoric stretches back to classical Greece. Today the term is most commonly taken pejoratively, meaning bombastic or exaggerated language. Every attempt to put words together includes choices about which words to use and how to arrange them. In this sense all writers, like it or not, use rhetoric. Rhetoric is also useful because it encourages thinking about one's audience.
Different audiences require different rhetorical choices.
In the following section, I'll list some of the most pertinent rhetorical techniques, or tropes, when writing for academic audiences. Different words, even if they ostensibly mean the same thing, have different connotations, as the poet W. H. Auden well understood. And different audiences have different expectations about appropriate diction. Academic writing requires a more formal diction than everyday talk or journalism, and within academe writing in the natural sciences requires a more formal diction than writing in the humanities. The layers of dirt were not messed up at all.