Hyperbole is deliberate exaggeration used for emphasis, surprise, or humor. Poets use it to make a feeling, image, or idea seem larger, stronger, or more dramatic than ordinary speech would allow.
It is not meant to be taken literally; its effect comes from the clear exaggeration.
Example
I waited a thousand years for your reply,
then carried my lonely heart across the sky.
The fish was a football field and a granny long.