Figurative language is a way of speaking or writing that uses things like similes and metaphors instead of sticking to the literal meanings of words. If your mom tells you to hold your horses, she's using figurative language.
The world would be a boring place without figurative language. If people only wrote literally, we wouldn't have lines like "Hope is the thing with feathers" and "I wandered lonely as a cloud." This poetic language isn't literally true, but it's deeply meaningful. You probably use figurative language all the time: "I'm up in the air about dinner." "I've got a mountain of homework." Figurative language, including simile, metaphor, allegory, and other figures of speech, makes our words come alive.