A monólogo is a dramatic speech delivered by a single character, allowing them to express their thoughts, emotions, and motivations directly to the audience. This device reveals inner conflicts and character depth, often serving as a window into their psyche. In the context of works like 'El burlador de Sevilla y convidado de piedra,' monólogos are crucial for understanding the complex nature of characters, especially in revealing their desires and moral dilemmas.