A one-person speech. Often used to express such emotions as love or sorrow. I use them to explain how much I am in love with this girl. They are popular in plays throughout history. One very famous monologue is Hamlet's "To be or not to be" speech.
I just wrote her a new monologue. Too bad she likes a jerkface. This one is about how I couldn't live without her...it's not as cliche as it sounds.