What is the difference between a monologue and a soliloquy?

AMonologues have been used for centuries in theater; soliloquies are a relatively recent innovation.

BMonologues tend to be longer and more philosophical; soliloquies are more brief and emotional.

CSoliloquies usually involve more than one character; monologues involve a character alone onstage.

DSoliloquies involve a character talking to herself; monologues may be addressed to someone.