Negation is the process that turns an affirmative statement (e.g. "I am American") into its opposite denial (e.g. "I am not American").
Negation takes on various forms in English, often not or its contraction -n't:
It was not feasible, in light of circumstances.
I didn't see it.
Sometimes it takes the form of an n- prefix (e.g. ever becomes never)
I have never eaten rabbit.
Other words which are commonly regarded as negations include hardly, barely, and scarcely; other negative prefixes include dis-, un-, and more.
Use the tag double-negation for questions regarding the use of two negations in a single clause.