What is the meaning of Negation?

The act of negating something.

A denial or contradiction.

A proposition which is the contradictory of another proposition and which can be obtained from that other proposition by the appropriately placed addition, or insertion, of the word "not". (Or, in symbolic logic, by prepending that proposition with the symbol for the logical operator "not".)

The logical operation which obtains such (negated) propositions.

A negative particle; a word, particularly an adverb, with a negative meaning: for instance, no and not in English, nōn, haud and nē in Latin, οὐ and μή in ancient Greek.

Source: wiktionary.org