Flag Officers are the top ranked officers in Star Command. The name has come about because of the requirement that the officer has an Alliance flag in their office at all times.
In the Fleet a Flag Rank officer in the field will have their own starship, which will be the flagship of whichever unit (task force, armada or fleet) they are assigned to unless someone of a superior rank is involved. They will not usually command the ship itself, leaving that to a Captain while they look at "the bigger picture."
When an officer reaches this rank they are amongst the elite, placed in charge of many units and with lots of demands on their time, as such they are awarded am attache, usually an officer who has shown command promise and can be seasoned by seeing "the bigger picture" and aiding a senior officer in organising their day and doing much of their paperwork.
The flag officer wear a golden braided aiguilette as part of their dress uniform.