准确来讲是：

(1)否定助动词(don't , doesn't , didn't 等) 来帮助句子构成否定句的，例如下面句子

They don't come from the same school.

Tom doesn't like being kept alone in the room.

Jack didn't come back from Beijing yesterday.

(2)否定副词：not与助动词(do, does, did)，情态动词(can, could, must, )一起构成否定助动词，并用来构成否定句，否定副词，可以直接否定动名词和不定式

Tom can't speak Chinese.

People are told not to take photos here.

Not having enough money, she can't buy the pen.

(3)否定词：本身具有否定含义的单个副词，例如seldom, little, few, hardly, nobody , nothing , none, nowhere, never, scarcely,

They seldom watch television these days.这些日子他们很少看电视。

He has never been abroad.他从未出过国。

We hardly know each other.我们彼此还不大认识呢。

       否定词有：neither, no, none, not, nor, nothing, never, nobody, no one, nowhere 等。

       广义否定词有：barely, hardly, rarely, scarcely, seldom 等。

       否定副词： no（用于一般疑问句答语开头）

      【说明】对于什么是否定副词，不同的语法书有不同的说法。作为英语学习者，没有必要计较其名称，只要知道词义和用法即可。