定语从句是修饰名词或代词的从句，通常由关系词（如that, who, whom, whose, which等）引导。在定语从句中，有些成分可以省略，包括：
1、关系词：当定语从句中的关系词在从句中作宾语或介词宾语时，可以省略不写。例如：The girl [whom/who] I met yesterday is my classmate. → The girl I met yesterday is my classmate.
2、被修饰的名词或代词：当定语从句中的主句主语就是被修饰的名词或代词时，可以将其省略。例如：I like the book that you recommended to me. → I like the book [that] you recommended to me.
3、动词be和情态动词：当定语从句中的谓语动词是be动词或情态动词时，这些动词也可以省略。例如：The man who is standing there is my uncle. → The man standing there is my uncle.
4、关系代词的部分：当定语从句中的关系代词带有指示功能的部分（如which, that, who等）可以省略。例如：This is the factory [which/that] we visited last year. → This is the factory we visited last year.
5、其他成分：当定语从句中包含了多个谓语动词或多个名词时，可以省略一些成分以简化句子。例如：The man [who is wearing a hat and reading a book] is my father. → The man [wearing a hat and reading a book] is my father.
需要注意的是，定语从句中的省略应该根据具体情况灵活运用，不能盲目省略，以免造成理解上的混淆。
定语从句省略的例句
1、The book [that] I read last night was really interesting. 昨晚我读的那本书真的很有趣。
2、The girl [who/whom] I met at the party is a doctor. 我在派对上遇见的那个女孩是一名医生。
3、The car [which/that] he bought yesterday is very expensive. 他昨天买的那辆车非常贵。
4、The restaurant [where] we had dinner last week was fantastic. 我们上周吃饭的那家餐厅非常棒。
5、The movie [that] we watched on Friday night was a thriller. 我们周五晚上看的那部电影是一部惊悚片。