Juxtaposition

Juxtaposition refers to the close placement of two items, traditionally to call attention to a contrast between the two items. Juxtaposition is sometimes confused with antithesis, which may use juxtaposition to illustrate a contrast between two ideas. To clarify: juxtaposition refers to the placement of the contrasting items, so it is a form of antithesis.

Definition of the Term
Juxtaposition - n. -
 * 1) an act or instance of placing close together or side by side, especially for comparison or contrast.
 * 2) the state of being close together or side by side.

Examples of the Term
A good source of juxtaposition examples is the Charles Dickens novel A Tale of Two Cities. Consider:
 * It was the best of times, it was the worst of times. (from opening lines of novel)

Another good source is Shakespeare's play Romeo and Juliet.
 * The youth of Juliet to the age of her nurse
 * The servants and the nobles