Metaphor

Metaphor: A figure of speech using an implied comparison of seemingly unlike things or the substitutin of one for the other, suggesting similarity. 

Example: 

"My mistress' eyes are nothing like the sun;"

              (Sonnet 130, Shakespeare"

This is a methaphor because he's comapring her mistress eyes to the sun. Even though he says that her eyes do not shine at all. He's comaring them to the sun and how they do not glow like it.