Polite negative non-past suffix attached to the -masu stem of a verb. Used in formal or polite speech.
See also: ます
私は肉を食べません。
I do not eat meat.
明日は学校に行きません。
I will not go to school tomorrow.
ません is the polite negative ending used in formal speech, while ない is the plain, casual negative form.
Derived from the polite auxiliary ます (masu) with the negative suffix ん (n), a contraction of the classical negative ぬ (nu).