(I. A. Richards, 1936: 100)
Metaphor is derived from the Greek verb that literally means ‘a carrying over’. When words are used metaphorically, one field of reference is carried over or transformed into another. In other words, a resemblance of two contradictory or different objects is made based on a single or some common characteristics.
In simple English, when you portray a person, place, thing, or an action as being something else, even though it is not actually that “something else,” you are speaking metaphorically. “He is the black sheep of the family” is a metaphor because he is not a sheep and is not even black. However, we can use this comparison to describe an association of a black sheep with that person. A black sheep is an unusual animal and typically stays away from the herd, and the person you are describing shares similar characteristics.
Aristotle’s definition of metaphor, however was very comprehensive: Metaphor consists in giving the thing a name that belongs to something else, the transference being either from genus to species, or from species to genus, or from species to species, or on ground of analogy’. It covered metaphor as well as Synecdoche and metonymy. And these three together with irony come to be considered the central tropes.
Furthermore, a metaphor develops a comparison which is different from a simile i.e. we do not use “like” or “as” to develop a comparison in a metaphor. It actually makes an implicit or hidden comparison and not an explicit one.