Use the idiom tag for questions which a dictionary cannot answer about set phrases with unusual meanings that can't be properly understood just from the separate words in them.
An idiom is a group of words established by usage as having a meaning not deducible from those of the individual words. Examples include:
- Rain cats and dogs (raining very hard; a deluge)
- See the light (suddenly understand, be enlightened)
- Put one's foot in one's mouth (say something carelessly that embarrasses oneself, often by offending another)
Idioms are usually grammatically correct sentences, but without context they make little to no sense. They are used to express a feeling or a belief in a way that a simple statement of fact cannot. ("I could eat a horse" or "I could eat a bear" carries more emotional and active feeling than "I need food".)