1. 定语从句的概念：在复合句中，用来修饰某一名词或代词的从句叫做定语从句。被定语从句修饰的名词或代词叫做先行词，定语从句必须放在先行词之后，对先行词起修饰限定作用。
e.g. He is the man who I want to see.
先行词 关系词 定语从句
2. 定语从句的引导词：
定语从句的引导词有关系代词that, which, who (whom, whose)和关系副词where, when, why两种，关系代词和关系副词放在先行词和定语从句之间，起联系作用，同时又在定语从句中充当一定成分。
3. 关系代词引导的定语从句：
① 如果先行词是表示人的名词或代词，关系代词应用who (whom, whose) 和that。
e.g. This is Xiao Wang who / that gave us a talk yesterday. (who / that在从句中作主语)
