An idiom is a phrase that means something different from what the individual words might suggest. When your friend says “it's raining cats and dogs,” no actual animals are falling from the sky: the phrase just means it's raining very hard. When someone says “break a leg” before your piano recital, they're wishing you good luck, not hoping you'll get injured.

Idioms make language colorful and expressive, but they can confuse people learning a new language because you can't figure them out by looking up each word separately. If you tell someone to “hold your horses,” you're asking them to slow down or be patient, even though no horses are involved. When something costs “an arm and a leg,” it just means it's very expensive.

Every language has its own idioms. In Japanese, people might say someone has “cat paws” to describe someone who seems harmless or inexperienced. English has thousands of idioms: “piece of cake” means something's easy, “under the weather” means feeling sick, and “spill the beans” means revealing a secret.

Learning idioms helps you understand how native speakers really talk. Without knowing idioms, you might understand all the words in a sentence but still miss what someone actually means.