While monologue and soliloquy both theoretically mean 'single speech', a monologue is a speech given by a person in the presence of others, while a soliloquy is a speech given by a person who is alone. Hope this helps! :)
Both soliloquys and monologues are speeches made by a single actor and are used by a playwriter to explain a character’s inner thoughts. However, a soliloquy reveals the thoughts a character wouldn’t say out loud to other characters in the play, while a monologue represents what a character would say to others. The thoughts expressed may not be inner thoughts and may just be what the speaker wishes to convey to the other characters.PLATO
