Definition - In linguistics, it is the quality that causes a statement to be deemed well-formed by a native speaker.

Oxford English Dictionary -
The term's first citation is from 1961:
"Within such a framework, deviance as well as grammaticality can tentatively be made explicit."
(A. A. Hill in Word XVII. 1 (title) Grammaticality. 1965 Language XLI. 403)

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