在复合句中，修饰某一名词或代词的从句叫做定语从句。被定从句修饰的词叫做先行词。定语从句必须放在先行词之后。引导定语从句的关联词有关系代词和关系副词。例如：
This is the present that he gave me for my birthday.
Do you know everybody who came to the party?
I still remember the night when I first came to the village?
This is the place where Chairman Mao once lived.
