What do we call a phrase that has a figurative meaning different from its literal meaning?

The correct answer is idiom. An idiom is a phrase or expression that carries a figurative meaning which is different from its literal interpretation. For instance, saying "it's raining cats and dogs" is not a literal statement about animals falling from the sky, but rather it means that it is raining heavily.

Understanding idioms is important because they often reflect cultural nuances and can add color to language. They are commonly used in everyday conversation, literature, and songwriting, making it essential for effective communication. Splitting idioms into their individual parts often leads to confusion, as the intended meaning is not derived from the words themselves but from the conventional usage in the language.

While similes and metaphors are figures of speech that make comparisons, they do not inherently carry the attribute of a fixed, culturally understood figurative meaning tied to the phrase as a whole. Proverbs, on the other hand, are short, generally known expressions that convey a truth or piece of advice but do not qualify as idioms based on the criteria given in this context.