The term "sullen" describes a mood or demeanor that is gloomy, silent, or withdrawn. A sullen person often appears unhappy or sulky, showing little interest in engaging with others. This behavior can be a response to disappointment, anger, or sadness, making it difficult for them to express their feelings openly. Sullen expressions can be observed in various situations, such as during teenage years when individuals may struggle with their emotions. In literature and film, sullen characters often add depth to the story, highlighting themes of isolation or inner conflict.