Define the term "soliloquy" and explain its purpose.

A soliloquy is a dramatic device in which a character speaks his or her thoughts out loud.

The purpose of such a device is to illustrate what is going on in the character's head in a way that can not be done quite as well through dialogue or action.  This can be very important in a play because the character's thoughts can be quite central to the development of the play.

For example, in Hamlet's "to be or not to be" soliloquy, we are given an insight into his psyche and we are allowed to understand what his thoughts are about life and death.