什么叫不定词？

不定词,infinitive,通常又称为不定式：一种动词的形式，起名词作用而又保持了某些动词的特征，如由副词来修饰。在英语中，不定式由to 引导，比如 愿意去是为了显示力量 或 我们希望他工作更加努力 ，也可不带 to ，如 她让他们看那封信 或 我们可以今天结束
A verb form that functions as a substantive while retaining certain verbal characteristics, such as modification by adverbs, and that in English may be preceded by to, as in To go willingly is to show strength or We want him to work harder, or may also occur without to, as in She had them read the letter or We may finish today

由to引导的句子，通常to后的动词用原形