Officer

An officer is a member of a group typically in the areas of the military, police, or some other form of authority. In a military service, an officer's typical role is to command and direct, maintain discipline and make plans and provisions for operation. Certain organizations have special criteria in order to achieve the status of officer.

Commission
In a military service, a commission is an order from the service's supreme authority, such as its commander-in-chief, authorizing an individual to legally hold a military rank, with all the privileges and responsibilities of said rank. A commission usually appoints an individual to hold an officer's rank.

In times of conflict, a temporary commission could appoint an officer to command rank to replace an incapacitated or killed commanding officer. Commander William T. Riker, for example, was granted a field commission promoting him to captain and given command of the USS Enterprise (NCC-1701-D) when the ship's commanding officer, Captain Jean-Luc Picard, was abducted and assimilated by the Borg during their first attempt to assimilate Earth. 

In situations where contact with Starfleet was not possible for very extended periods, a commanding officer had the authority to grant commissions to officers under his or her command, or revoke their existing commissions; that is, he/she had the authority promote or demote his/her officers. Good examples of this are when Captain Kathryn Janeway, commanding officer of the USS Voyager, promoted her chief tactical officer and security chief, Lieutenant Tuvok, to the higher rank of lieutenant commander, or when she demoted her flight controller, Lieutenant Junior Grade Tom Paris, to ensign. . After a year of exemplary service, she reinstated him to his former rank. 

Starfleet
In the Federation Starfleet, an officer or commissioned officer was an individual who had attended and graduated from the four-year cadet program of Starfleet Academy. Upon graduation from the Academy, the cadet was granted a commission appointing him or her to Starfleet's most junior officer's rank: that of ensign. With the commission came a Bachelor's degree in his or her major field of academic study, be it the pure sciences, medicine, military science, etc.

Commissioned officers are distinguished from non-commissioned officers and other crewmembers through the use of a rank structure.

Commissioned officer rank structure
Starfleet ranks from lowest to highest:
 * 1) Ensign
 * 2) Lieutenant junior grade
 * 3) Lieutenant
 * 4) Lieutenant commander
 * 5) Commander
 * 6) Captain
 * 7) Commodore (aka rear admiral, lower half)
 * 8) Rear admiral (upper half)
 * 9) Vice admiral
 * 10) Admiral
 * 11) Fleet admiral

Other officer terms

 * Certain officer positions could be filled by non-commissioned officers and civilians if the need arose.

By rank

 * Field officer
 * Flag officer
 * Line officer
 * Ranking officer
 * Commissioned officer
 * Provisional officer
 * Non-commissioned officer

By title

 * Senior officer (see also: senior staff)
 * First officer
 * Second officer
 * Third officer

By command structure

 * Commanding officer
 * Executive officer
 * Duty officer

By department

 * Helm officer
 * Navigator
 * Operations officer
 * Engineer
 * Tactical officer
 * Security officer
 * Weapons officer
 * Armory officer
 * Intelligence officer
 * Communications officer
 * Medical officer
 * Science officer
 * Counselor

By function

 * Bridge officer
 * Records officer
 * Morale officer
 * Liaison officer
 * Convoy liaison officer
 * Fleet liaison officer
 * Strategic operations officer
 * Archaeology and anthropology officer
 * Personnel officer
 * Police officer

Offizier Oficial Comisionado Officier 士官 Officier