Not can be an adverb, conjunction, interjection, or a noun. As an adverb, it means "not doing" or "not performing". As a conjunction, it joins phrases or clauses together and usually has the meaning of "nor" or "or". As an interjection, it is used to express astonishment, joy, etc., and is usually followed by an exclamation mark. Finally, as a noun, it means the negative form of some word or group of words.