顾名思义，后置定语就是定语在所修饰词的后面，短语、句子都可以作后置定语，甚至某些情况下，单词也可以作后置定语。如：

There is something wrong with the machine.(单词wrong作后置定语，修饰something)

The man standing under the tree is my brother.(短语作后置定语)

The man who is standing under the tree is my brother.(句子作后置定语，定语从句)。