Imperial Highness

Imperial Highness is a style used by members of an imperial family to denote imperial – as opposed to royal – status to show that the holder in question is descended from an emperor rather than a king.

When used as a direct form of address, spoken or written, it takes the form Your Imperial Highness. When used as a third-person reference, it is gender-specific (His Imperial Highness or Her Imperial Highness, both abbreviated HIH) and, in plural, Their Imperial Highnesses (TIH).