A flag rank is one of naval officer ranks that permit its holder to fly a flag to represent where he exercises his command. This commonly means the ranks of Rear-Admiral, Vice Admiral, Admiral, or Admiral of the Fleet.
The term can also be used as part of the title of a post; e.g. Flag Officer Liverpool.
In United Kingdom usage, equivalent ranks in the Army and Royal Marines are called General Officers, and those in the Royal Air Force are called Air Officers