Question

Imagine that you are watching a play, and in the middle of the scene all of the characters quietly walk offstage except one. The lights go down and a spotlight shines on the one character remaining on stage. The character begins a very serious-sounding speech, as if talking to himself. What is happening?

Answer 1

It depends. It's either a monologue or a soliloquy, if it's one person.

Both a monologue and a soliloquy are lengthy discourses made by one person. The difference is that a soliloquy is when the character is speaking to himself, without awareness of the presence of others. In a drama it's usually a device meant to reveal the character's innermost thoughts. It's talking while the character is alone or as if he is alone. The speaker of a monologue, while monopolizing the conversation, is speaking to others.

The origin of the word "monologue" is Greek "monologos" - speaking alone. The origin of soliloquy is Latin "soliloquium" - talking to oneself.
Source:
I wish I could say this was my own answer bc it's a lovely answer but I copied and pasted most of it from: http://www.answerbag.com/q_view/387737