Wikia

Fleet Admiral is a military rank, the equivalent of which is used by the service organizations of many civilizations. As a traditional grade, Fleet Admiral is the most senior Flag Officer rank of a naval organization, above the grade of Admiral and the other Flag Officer grades. The Commander-in-Chief of the Starfleet Operating Forces, Commander of Vanguard Command, and the Commander, Starfleet are all Fleet Admirals.

In comparison to infantry ranking systems, this rank is equivalent to the most senior General rank.