A figure of speech is an indirect way of communicating an idea. Many figures of speech are not meant to be understood exactly as they are said: they are not literal, factual statements. They use indirect language, and mean something different from ordinary language.
Linguists call these figures of speech "tropes"—a play on words, using words in a way that is different from its accepted literal or normal form. DiYanni wrote: "Rhetoricians have catalogued more than 250 different figures of speech, expressions or ways of using words in a nonliteral sense".[1]
Metaphors are very common examples. A common figure of speech is to say that someone "threw down the gauntlet". This does not mean that a person threw a protective wrist-covering down on the ground. Instead, it usually means that the person issued a public challenge to another person (or many persons).
There is no one easy way to distinguish plain speech from figures of speech.[2]