If you dream about a play, the mood of the play can represent emotions that you are feeling in waking life.
The plot and the characters in the play can symbolize aspects of yourself.
Watching a play in a dream can also be a sign that you want to escape from the stresses of your waking life.
A dream in which the dream takes the form of a play, and you are observing it all as a member of the audience is a common type of lucid dream.