Imperial Majesty (His/Her Imperial Majesty, abbreviated as HIM) is a style used by emperors and empresses. It distinguishes the status of an emperor/empress from that of a king/queen, who are simply styled Majesty (HM). Holders of this style have sometimes been observed to follow religious leaders who are styled "His Holiness" in public ceremonies.
King-Emperors and Queen-Empresses sometimes have used the style Imperial and Royal Majesty (e.g. The Empress Frederick's style Her Imperial and Royal Majesty The German Empress and Queen of Prussia).
Incongruously the Emperor of Japan no longer uses the style Imperial Majesty (preferring the Royal title of "Majesty") despite Imperial usage by the rest of his household, as made clear by the Imperial Household Agency of Japan.