脾气 (pí qi) refers to a person's temper or disposition, especially how easily they get angry (e.g., 发脾气 'lose one's temper'). It is more specific than 性格 (xìng gé), which means overall personality or character, and 气质 (qì zhì), which describes a person's demeanor or presence. 脾气 is commonly used in everyday speech for moods and anger.