A colloquialism is an informal expression, that is, an expression not used in formal speech or writing. Colloquialisms can include words (such as "gonna" or "grouty"), phrases (such as "ain't nothin'" and "dead as a doornail"), or sometimes even an entire aphorism ("There's more than one way to skin a cat"). Dictionaries often display colloquial words and phrases with the abbreviation colloq. Colloquialisms are often used primarily within a limited geographical area.

In some areas, overuse of colloquialisms by native speakers is regarded as a sign of substandard ability with the language. However, in the mouth of a non-native speaker, they are sometimes taken as signaling unusual facility with the language as they may be more difficult for non-native speakers to understand.

A colloquialism can sometimes make its way into otherwise formal speech, as a sign that the speaker is comfortable with his or her audience, in contrast to slang, which if used in formal speech is more likely done so consciously for humorous effect.

See also

• Slang
• Jargon
• Idiom
• Variety (linguistics)