Symbolism is a device in which an object, person or situation is given another meaning beyond its literal one--usually something more abstract or non-rational than the symbol itself. There are many kinds of symbols. Normally, dramatists weave clues into the work to indicate that certain elements are intended to be taken as symbolic.
There are two main categories of symbols: universal symbols and contextual symbols. Universal symbols have meaning across many different works. For example, snakes often express cunning and treachery all throughout literature. Contextual symbols, on the other hand, only have meaning within the work in which they are featured.
There are several types of symbols. Metaphor is an implicit identification of one thing with another without the use of a verbal indicator. For instance, saying "he is an animal." Similes are similar to metaphors, but they use a verbal indicator ("he eats like a pig"). Allegory is an extended metaphor that lasts the entirety of the work. An archetype is a character or plot element that occurs throughout myth. For example, the appearance of angels as beings with wings and halos. Personification, the attribution of human characteristics to non-human entities, is a subset of symbolism.
Symbolism adds depth to a dramatic work. It causes audiences to reflect more thoroughly upon what they have seen. Symbolism is also a powerful force for communicating meaning; certain themes or ideas affect the mind of the audience more profoundly when presented indirectly through a symbol than when presented overtly.