What is a metaphor?

metaphor
ˈmɛtəfə,ˈmɛtəfɔː/
noun
noun: metaphor; plural noun: metaphors
  1. a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable.
    “when we speak of gene maps and gene mapping, we use a cartographic metaphor”
    synonyms: figure of speech, figurative expression, imagetropeallegoryparableanalogycomparisonsymbolemblem, word painting, word picture;

    literaryconceit
    • a thing regarded as representative or symbolic of something else.
      “the amounts of money being lost by the company were enough to make it a metaphor for an industry that was teetering”
Origin
late 15th century: from French métaphore, via Latin from Greek metaphora, from metapherein ‘to transfer’.