A word or phrase for one thing that is used to refer to another thing in order to show or suggest that they are similar.

An object, activity, or idea that is used as a symbol of something else.

A figure of speech in which a word or phrase literally denoting one kind of object or idea is used in place of another to suggest a likeness or analogy between them
A metaphor is a figure if speech that describes a subject by asserting that it is, on some point of comparison, the same as another otherwise unrelated object. Metaphor is a type of anology and is closely related to other rhetorical figures of speech that achieve their effects via association, comparison or resemblance including allegory ,hyperbole  and simile.