就是用来修饰英语名词的词语或者句子,比如漂亮的女孩,beautiful girl中的beautiful就是一个形容词做定语,但是英语中还有后置定语定语从句的用法,比如我写的信,the letter written by me这个 written by me就是一个分词短语作后置定语,再比如你回答的问题,the question that is answered by you,这个that is answered by you就是一个定语从句,是一个句子修饰名词.