Figures of speech
The term figures of speech refers to the ways in which language is used imaginatively, or creatively. (There is an adjective to convey this idea, figurative. The opposite, in this sense, is literal - see Literal - figurative.) The key aspect of the idea is that figures of speech (sometimes simply called figures, and in the past often called tropes) break the usual rules of simple communication in some way, in order to make the language more striking. OED gives two definitions, at meanings 21 and 22 of 'figure': "Rhet. a. Any of the various 'forms' of expression, deviating from the normal arrangement or use of words, which are adopted in order to give beauty, variety, or force to a composition; e.g. Aposiopesis, Hyperbole, Metaphor, etc. Also, figure of speech." The second is: "a. Grammar. Any of the permitted deviations from the normal forms of words (e.g. Aphaeresis, Syncope, Elision), or from the ordinary rules of construction (e.g. Ellipsis) ... Formerly also figure of speech." In these definitions, you will notice that in the fields of both grammar and rhetoric, figures of speech are 'deviations' from the norm, which are nevertheless 'permitted'. In rhetoric, which is 'the art of persuasion', it is stressed that figures are used to make writing (or speaking) more beautiful, varied or more powerful. In general the intention is to use words in a creative or interesting way.
The figurative use of language is to be contrasted with the literal use of language, where words mean no more and no less than their basic meaning. It is actually very rare in normal human language to come across more than a few words without any figurative language. Often these are dead or fossilised metaphors. There is a Science Fiction story by Isaac Asimov in which a great logical problem is caused when a human who is annoyed with a robot tells it to "Get lost!" and it understands him literally. (How can one find an intelligent machine that is trying not to be found? The man of course was using a dead metaphor.)
In the AWE guide, some of the basic ideas about Figures of Speech' are grouped to construct a course in teaching students the principles - see Figures of Speech course for the first step. The category ' may help you navigate round many of the types that have been named by diligent scholars in the past. (In older times there was much discussion about how to classify the different figures of speech. Much of this discussion is sterile; some seems wrong-headed to AWE; some just wrong; for an example, see Syllepsis - zeugma.) You are unlikely to need most of these, and many are not included in the AWE project.