Metaphor: a short similitude; a figure of speech in which a word or phrase is applied to an object. 

For example: The soldier was a lion in combat.  

From Greek μεταφερω (to transfer), which further derives from μετα (over) and φερω (carry). 

Mixed metaphors are fun. 

• It’s not rocket surgery.
• We’ll burn that bridge when we come to it.
• Half of one, six dozen of another.
• Robbing Peter to pay the piper.
• Trying to thread a needle with a haystack.
• Burning the midnight oil at both ends.
• Don’t beat a dead horse in the mouth.

Some people don’t get metaphors.  The meaning goes right over their head.  Not me.  Nothing goes over my head.  I’m too tall, and my reflexes are too fast.