Hochgeboren is a form of address for members of the highest German nobility. It translates to High Born or of High Birth. The actual address is "Euer" Hochgeboren. It is the correct form of address for German high nobility: princes, dukes, and counts.
The title should not be confused with (Euer) Hochwohlgeboren, which ranks lower, and is the correct form of address for German barons, knights, and Freiherren; or (Euer) Wohlgeboren, which ranks lower than Hochwohlgeboren, and is the address for a Vogt or Büttel.