Figure of speech

OK - I ran yesterday's post past my grandchildren and their immediate response was "I know the word, but exactly what is a metaphor?".  Good grief, what do they teach children these days?  So here's grammar 101.  A simile is when you compare one thing with another.  A metaphor is when you talk about one thing as though it were another.  So "the moon crossed the sky like a ship under sail" is a simile - comparing the moon to a sailing ship.  "The moon sailed across the sky" is a metaphor, treating the moon as though it were a sailing ship.  So a metaphor is always a fantasy - the moon cannot really sail any more than a person can really be on tenterhooks.