Pronouns are often used to refer to a noun that has already been mentioned.

pronouns 是 pronoun 的复数形式。pronoun 由前缀 pro-（表示"代替"）和 noun（名词）组成，字面意思是"代替名词的词"，即"代词"。 在语法中，代词用于替代之前已经提到过的名词，以避免重复。