Admiral

Admiral is a navy rank given to an officer who commands a fleet of ships.

In Star Wars

An admiral is a flag rank above Line-captain and Commodore. Due to the size of the Imperial fleet, several classes of admiral exist that each represent different ranks. Admirals do not command a single ship, their responsibilities lie entirely at the fleet level and above. Admirals draw up invasion plans, organize supply transfers, and otherwise tend to keep themselves occupied at the higher levels of fleet function.

In Star Trek

In the Federation Starfleet, admirals appear to be largely desk officers, commanding groups of ships from ships only in times of war due to the largely dispersed nature of the fleet in peacetime. Oddly enough, the supposed Federation flagship Enterprise is almost never occupied by a Flag officer of any rank.