A soliloquy is a long speech in which a character speaks one’s thoughts to the audience.
When a character makes a speech when he is alone is known as a soliloquy. The plays of Shakespeare's are full of soliloquies. They tell the audience about the inner thoughts o the character. The plotting about a revenge or any murder and lamentations on one's fate are the main soliloquies. Usually, soliloquies are said by the characters when they are alone.