An idiom (Latin: idioma, "special property", from Greek: ἰδίωμα – idíōma, "special feature, special phrasing, a peculiarity", f. Greek: ἴδιος – ídios, "one’s own") is a phrase or a fixed expression that has a figurative, or sometimes literal, meaning. An idiom's figurative meaning is different from the literal meaning.[1] There are thousands of idioms, and they occur frequently in all languages. It is estimated that there are at least twenty-five thousand idiomatic expressions in the English language.[2] Idioms fall into the category offormulaic language.

EXAMPLES: The following sentences contain idioms. The fixed words constituting the idiom in each case are bolded:[3]

1. She is pulling my leg. - to pull someone's leg means to tease them by telling them something untrue.2. When will you drop them a line? - to drop someone a line means to send a note to or call someone.3. You should keep an eye out for that. -to keep an eye out for something means to maintain awareness of it so that you notice it as it occurs.4. I can't keep my head above water. - to keep one's head above water means to manage a situation.5. It's raining cats and dogs. - to rain cats and dogs means to rain very heavily (a downpour).6. Oh no! You spilled the beans! / you let the cat out the bag - to spill the beansmeans to let out a secret.7. Why are you feeling blue? - to feel bluemeans to feel sad.8. That jacket costs an arm and a leg. –an arm and a leg means a large amount of money.9. It is not rocket science. – not rocket science means something is not difficult.10. Put a cork in it. - put a cork in it is an another way to say, "shut up!" (another idiom), be quiet, and stop talking.11. I'm screwed. - to be screwed means that one is doomed, is in big trouble, or has really messed up.12. I bet and/or I'll bet. - I bet and I'll betare sarcastic ways of saying "certainly" or "of course".

Each of the word combinations in bold has at least two meanings: a literal meaning and a figurative meaning. Such expressions that are typical for a language can appear as words, combinations of words, phrases, entire clauses, and entire sentences.

l. The devil is in the details.m. The early bird gets the worm.n. Break a leg.o. Waste not, want not.p. Go take a chill pill.q. I have butterflies in my stomach.

Expressions such as these have figurative meaning. When one says "The devil is in the details", one is not expressing a belief in demons, but rather one means that things may look good on the surface, but upon scrutiny, undesirable aspects are revealed. Similarly, when one says "The early bird gets the worm", one is not suggesting that there is only one worm, rather one means there are plenty of worms, but for the sake of the idiom one plays along, and imagines that there is only one worm; alternatively, the figurative translation of this phrase is that the most attentive and astute individual, or perhaps the hardest working (or simply the first one) gets the desired outcome to a situation or the better product, depending on the context. On the other hand, "Waste not, want not" is completely devoid of a figurative meaning. It counts as an idiom, however, because it has a literal meaning and people keep saying it.