"Metaphor" means understanding one thing in terms of another. This can be explicit or subtle. Sometimes—often?—metaphors are such a deep part of our psyche that we're unaware that we are using a metaphor at all. For instance, describing an argument in terms of war, or an idea in terms of a structure or building. Metaphors form coherent systems: when a concept is described using different metaphors, these usually fit together in a logical way.
[[Lakoff and Johnson - Metaphors We Live By|Lakoff, George, and Mark Johnson. Metaphors We Live By. University of Chicago Press, 2008.]]