A police officer (also called a policeman or policewoman, a cop, or less commonly a constable), is a warranted law employee of a police force. In most countries, "police officer" is a generic term not specifying a particular rank. In some, the use of the rank "officer" is legally reserved for military personnel.
Police officers are generally charged with the apprehension of suspects and the prevention, detection, and reporting of crime, protection and assistance of the general public, and the maintenance of public order. Police officers may be sworn to an oath, and have the power to arrest people and detain them for a limited time, along with other duties and powers. Some officers are trained in special duties, such as counter-terrorism, surveillance, child protection, VIP protection, civil law enforcement, and investigation techniques into major crime including fraud, rape, murder, and drug trafficking. Although many police officers wear a corresponding uniform, some police officers are plain-clothed in order to pass themselves off as members of the public. In most countries police officers are given exemptions from certain laws to perform their duties. For example, an officer may use force if necessary to arrest or detain a person when it would ordinarily be assault. In some countries, officers can also violate traffic code to perform their duties.
The word "police" comes from the Greek politeia, meaning government, which came to mean its civil administration. The more general term for the function is law enforcement officer or peace officer. A sheriff is typically the top police officer of a county, with that word coming from the person enforcing law over a shire. A person who has been deputized to serve the function of the sheriff is referred to as the deputy.
Police officers are those empowered by government to enforce the laws it creates. In The Federalist collection of articles and essays, James Madison wrote: "If men were angels, no Government would be necessary". These words apply to those who serve government, including police.