hyperbole:
Figure of speech using deliberate exaggeration or overstatement. Not intended literally, hyperbole may be humorous or serious

Example:
"Your beauty, that did haunt me in my sleep
to undertake the death of all the world,
so I might live one hour in your sweet bosom"
-Shakespeare, Richard lll

Explanation:
In this quote Shakespeare over-exaggerates the beauty of a woman. The purpose of this is to exemplify her beauty, and show the main character is distracted by it. This type of exaggeration helps the reader characterize the woman. Also the purpose is to emphasize her, and show what the main character will do because of this.