1.定语：定语用来限定、修饰名词或代词的，是对名词或代词起修饰、限定作用的词、短语或句子，汉语中常用‘……的’表示。

a clever boy The boiling water Fallen leaves The man who you are looking for

2.定语从句：修饰某一名词或代词的从句。

Do you know the man who came to see Xiao Yang this morning?