A simile is a comparison using either "like" or "as."
John swaggers like a pirate since he has gone off to college.
The simile is acutally a gentle kind of metaphor since it softens its comparison with a buffer word ("like" or "as").
Consider the following lines from Lord Byron:
The Assyrian came down like a wolf on the fold
And his cohorts were gleaming in purple and gold.
By comparing the Assyrian warrior to a wolf (and his opponents to a fold of sheep), Byron transfers all of the bestial strength and aggressiveness that is traditionally associated with a wolf to the Assyrian, whom he clearly dislikes.
The simile is very important to poety, but it can also be found frequently in prose where it is sometimes difficult to handle. One of the short story writers who handles simile most effectively (or gets away with it, if you like) is Flannery O'Connor. Consider the opening line of her story "Greenleaf":
"Mrs. May's bedroom window was low and faced on the east, and the bull, silvered in the moonlight, stood under it, his head raised as if he listened—like some patient god come down to woo her—for a stir inside the room."
Can you identify the two terms (A and B) of the simile? See if you can reconstruct the sentence using a metaphor instead of O'Connor's simile. (You need to leave out only one word.) Is your new sentence stronger than the original?