Officer

A Pirate Officer is a high-ranking member of a pirate crew that command lesser crew members.

Role and Duties
Pirate Officers are members of pirate crews that are trusted enough by the captain/admiral to be given authority over the rest of the crew. They issue commands to other crew members but still answer to the crew's leader. There can also be officers that have authority over other officers, such as the elite officers of the Donquixote Pirates.

Pirate Officers are usually the stronger fighters of a pirate crew, but sometimes fill out other professions besides fighting. For example, Nami was an officer of the Arlong Pirates, but mostly acted as the crew's navigator than anything else.

Also, the term "officer" is not always used for high-ranking pirate crew members, such as the Beasts Pirates have "headliners", whose role is basically the same as an officer's.