Metaphor is probably the most complicated figure of speech.
It is derived from the Greek word for transfer (Nims 24), comparing
two things directly like "A is B," or it even ignores the verb and implies
that A is B. It differs from Simile for its not using words like "like,"
and from Symbol for "[t]he two terms of a metaphor must resemble each other,
even if only incidentally, but a symbol usually has no physical
characteristics at all to justify its abstract meaning. Metaphor is
a matter of identifying two things with each other. In symbolism,
however, the symbolic object and its significance are thought of
as clearly separate things, the one concrete, the other abstract.
Further, symbolism tends to remain fixed; once a symbol has acquired
a certain value, it tends to keep it. This characteristic makes
symbols particularly useful in extended works of literature like
novels or plays" (Korg 68).
  There are several possibilities for Metaphor: by usage could divide
into "metaphor," "conceit," and "juxtaposition." The simpler metaphor
concerns "A is B," like "he is a stallion"; and the more complicated
one rids of the verb, like what Pound does in his "In the Station of
Metro," or Robert Francis in his "The Hound." As for the other two
entities of metaphor, the reader may find Donne's "The Flea" and Henry
Reed's "Naming of Parts" quite typical.
  To sum up, Metaphor is actually a flexible way of showing analogies.