Metaphor:

A relation between two symbols, which may be simple juxtaposition (literal metaphor), a rhetorical statement of likeness or similarity (descriptive metaphor), an analogy of proportion among four terms (formal metaphor), an identity of an individual with its class (concrete universal or archetypal metaphor), or statement of hypothetical identity (anagogic metaphor).

so i’m guessing that a literal metaphor is “a relation between two symbols, which may be simple juxtaposition” =]

i had to look up juxtaposition myself, so i pasted it in anyways.

jux·ta·po·si·tion

–noun 1. an act or instance of placing close together or side by side, esp. for comparison or contrast.

i hope i helped.