The answer is:
Speaking to one's self out loud without regard to who might be listening
A soliloquy is a way of communicating the actors thoughts and feelings to the audience as if they were just reflections by the actor himself, almost like reading the actor's mind. The actor speaks out loud, but she is either alone or presumably unheard by other characters on stage. She is not addressing the audience, but the play is giving the audience a window into the actor's mind.
