In literature, the serious and extensive use of symbols.
Symbol - A person, place, or object that represents something beyond itself. Symbols can succinctly communicate complicated, emotionally rich ideas.
Massachusetts English Language Arts Curriculum Framework June 2001
Grasp the meaning of "symbol"
Just as the American bald eagle is often thought of as the symbol of the United States, symbols used in literature are objects used to represent other things or ideas. For example, in Hawthorne's "The Scarlet Letter," the "A" that Hester Prynne was forced to wear represented not only that she was an adulteress, but also the first letter of the name of her illegitimate child's father, the Reverend Arthur Dimmesdale.
There are several ways to recognize symbolism in literature. One is the frequency an object or character is mentioned in a piece of literature--if it is mentioned often, it is probably important. Another way to find a symbol is to look at how much detail is used in describing an object. These two methods give clues that the writer wants you to infer something about a particular object.
Familiarize yourself with the author's work and style
A symbol in a piece of literature often represents an important issue of the time in which the author lived, or has personal significance to the writer. Edgar Allan Poe, for example, is well-known for the tragedy he suffered during his lifetime. His stories and poetry often included dark imagery and death which were undoubtedly symbolic of the events in his life.
If an image or object described by the author makes you react in a certain way, you are probably on to something, never discredit your own feelings just because you're a novice. It is very likely that the author planted the image in the work in a particular way to alert the reader that a symbol is important.
There's no shame in reading critical essays about a literary work to gain a better understanding of it, or in discussing a piece of literature with a teacher or classmate. With experience, finding symbols will become easier, but when you are first starting out, it never hurts to get ideas from others who have a better grasp of symbolism.