IDIOMATIC EXPRESSIONS: What is an idiomatic expression? An idiomatic expression or an idiom is a group of words established by usage as having a meaning not deducible from those of the individual words.
Using, containing, or denoting expressions that are natural to a native speaker.
Examples: 1. It's raining cats and dogs. 2. That's a blessing in disguise. 3. To Get up on the wrong side of the bed.