I’m the treaty of Ghent 1814 what does “Britannic majesty” mean?

On December 24, 1814, The Treaty of Ghent was signed by British and American representatives at Ghent, Belgium, ending the War of 1812. By terms of the treaty, all conquered territory was to be returned, and commissions were planned to settle the boundary of the United States and Canada.

Her Britannic Majesty, or His Britannic Majesty depending on the gender of the monarch, is a treaty title for the monarch of the United Kingdom, a royal style used in international law and diplomacy. It is used on the international plane in the same way that His Majesty or Her Majesty is used to refer to the king or queen domestically, the addition of Britannic serving to identify the state (United Kingdom) in question. It is particularly used in treaties and other formal instruments sent and received between nations. Many other monarchies in Europe used similar conventional terms as treaty titles to identify their respective monarchs.