陛下 is a formal, honorific pronoun used in historical or ceremonial contexts to address or refer to an emperor, equivalent to 'Your Majesty' (direct address) or 'His/Her Majesty' (third-person reference). It appears in dialogues from ancient China or in modern historical narratives. Unlike the English 'Majesty' which can be used with a king or queen, 陛下 is specifically reserved for emperors in Chinese tradition.