Officer

An Officer is a high-ranking member of any group (besides the Marines) that command lower-ranking members.

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

Officers are usually the stronger fighters of an organization, 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.