A metaphor is described as "a figure of speech that makes a comparison between two things that are basically dissimilar."1 In other words, it describes one thing in terms of another. It is comparative, and thus goes beyond a mere descriptive adjective (e.g. the "bright moon" is not a metaphor). A metaphor describes one object as being or having the characteristics of a second object. Unlike a simile, a metaphor "does not use connective words such as like, as, or resembles in making the comparison."2
Examples of metaphor include "life is a dream" (describing life in terms of a dream), "the foundation of knowledge" (knowledge in terms of house construction), and "he was scraping the bottom of the barrel" (a lack of talent described in terms of a barren fruit container). A metaphor that is extended throughout a poem or story, and may involve further related comparisons, is an extended metaphor. If we use a metaphor so often that we don't realize it, the phrase may become a "dead" metaphor (e.g. "foot of the hill," "leg of the chair").
Sometimes metaphor is defined in very broad terms, and is used as another term for "figurative language" or "figure of speech". In this sense, "metaphorical language" incorporates all comparative language, including similes and symbols. For your English exams, however, it is safer to use the more formal phrase "figurative language."
It can be argued that human communication is intrinsically metaphorical, and that human communication as we know it couldn't exist without metaphor. Some have argued that our most essential mental concepts (e.g. time and space) are inherently suffused with metaphorical descriptions, so that "the way we think, what we experience, and what we do every day is very much a matter of metaphor."3 It does seem that metaphors are part of our everyday discourse. Below is a metaphor that is both linguistic and visual, and is commonly used in literature and current affairs. What is the metaphor?
In the cartoon above, the embarrassment of US abuse of Iraqi prisoners is considered to be a "stain" on America's reputation. Thus, moral embarrassment or guilt is described in terms of an ugly stain. It echoes Lady Macbeth's cry of "Out damn spot!" (Uncle Sam and the flag are symbols of the United States, and thus, in a broad sense, also metaphors.)
1. Damrosch, Leopold
et al., Adventures in English Literature (San Diego: