An officer is a person who holds a high rank in a uniformed organisation like the military or police. A military officer has a commission, a state document saying others must obey him. Some examples of officer ranks would include captains, majors, and lieutenants, but not sergeants, who are sometimes called non-commissioned officers, or NCOs.

People who are in a position of importance in an organization or company may be a corporate officer, for example:

• The Chief Executive Officer (CEO) of a company is the person in charge of that company.
• In many organizations, the officers are the president, vice-president, secretary and treasurer. These people run the organization, keep track of what goes on at meetings and handle the money for the organization.