Define the term "soliloquy" and explain its purpose.
As stated in the other answers, a soliloquy is a dramatic convention in which a character, usually alone on stage or at least not heard by other characters on stage, speaks their thoughts aloud. The purpose of a soliloquy is to give an audience insight into the psychology of a character, including their reasons for doing something (or avoiding doing something). Through a soliloquy, a playwright presents significant "internal" information that an audience needs to understand, similar to the way a writer might use an omniscient narrator. For example, Shakespeare employs a number of soliloquys in Macbeth to help the audience understand the motivations and fears of his characters. The following soliloquy appears in Act 1, Scene 7 of Macbeth, and is spoken by Macbeth as he considers (and reconsiders) the plan to kill King Duncan:
"If it were done when ’tis done, then ’twere well
It were done quickly: if the assassination
Could trammel up the consequence, and catch
With his surcease success; that but this blow
Might be the be-all and the end-all here,
But here, upon this bank and shoal of time,
We’ld jump the life to come. But in these cases
We still have judgment here; that we but teach
Bloody instructions, which, being taught, return
To plague the inventor: this even-handed justice
Commends the ingredients of our poison’d chalice
To our own lips. He’s here in double trust;
First, as I am his kinsman and his subject,
Strong both against the deed; then, as his host,
Who should against his murderer shut the door,
Not bear the knife myself. Besides, this Duncan
Hath borne his faculties so meek, hath been
So clear in his great office, that his virtues
Will plead like angels, trumpet-tongued, against
The deep damnation of his taking-off;
And pity, like a naked new-born babe,
Striding the blast, or heaven’s cherubim, horsed
Upon the sightless couriers of the air,
Shall blow the horrid deed in every eye,
That tears shall drown the wind. I have no spur
To prick the sides of my intent, but only
Vaulting ambition, which o’erleaps itself
And falls on the other."
Through this soliloquy, the audience gains insight into the inner conflict that Macbeth feels over the upcoming murder. He gives a number or reasons why he doesn't want to murder Duncan: the act won't stand alone, but will lead to other repercussions like eternal damnation, it would set a precedent for regicide (which could return on Macbeth when he is king), and he should be protecting the king rather than plotting Duncan's demise. By employing this technique, Shakespeare lets his audience see the deeper, more human aspects of Macbeth, thus preventing the character from being a one dimensional "bad guy" and allowing the audience to see him as a conflicted, tortured soul. At the end of the soliloquy, Macbeth states that his ambition still takes precedence, thus allowing the audience to understand his tragic flaw. The use of this and other soliloquies ensures that Macbeth's eventual downfall is all the more effective on the audience because they have been given prior insight into his initial, far less selfish nature and can understand the pitfalls associated with ambition, something seen as positive.
A soliloquy is a literary device used by writers to give insight into a character's inner feelings. By definition, it is a dramatic convention in which a character, usually alone on stage or at least not heard by other characters on stage, speaks his thoughts aloud. Soliloquies are usually meant for the audience's ears only and informs them about the character's motivations and state of mind. A similar literary convention is an "Aside," in which the speaker directs his dialog to the audience while members onstage are unable to hear. Shakespeare's "To be or not to be" speech in Hamlet is probably the most famous example of a dramatic soliloquy. (The Bedford Introduction to Literature, 6th Edition)
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.