Synecdoche:
A figure of speech in which a part of something stands for a whole of something.


Example:
"The world treated him badly."

Explanation:
This quote is saying that the "world" treated him badly, which is impossible. The purpose of synecdoche is to emphasis something. In this case how badly "he" was treated, since its described as the world treating him badly, this shows that he was treated very badly. This concept can be applied to literature and poetry, the author wants to emphasis something by making more than one thing into one.