A police force is a constituted body of persons empowered by a state to enforce the law, to protect people and property, and to prevent crime and civil disorder. Their powers include the power of arrest and the legitimized use of force. The term is most commonly associated with police services of a sovereign state that are authorized to exercise the police power of that state within a defined legal or territorial area of responsibility. Police forces are often defined as being separate from military or other organizations involved in the defense of the state against foreign aggressors; however, gendarmerie are military units charged with civil policing. The police force is usually a public sector service, funded through taxes.
Law enforcement is only part of policing activity. Policing has included an array of activities in different situations, but the predominant ones are concerned with the preservation of order. In some societies, in the late 18th and early 19th centuries, these developed within the context of maintaining the class system and the protection of private property. Police forces have become ubiquitous in modern societies, though some are involved to varying degrees in corruption, police brutality and the enforcement of authoritarian rule.
As police are often interacting with individuals, slang terms are numerous. Many slang terms for police officers are decades or centuries old with lost etymology. One of the oldest, "cop", has largely lost its slang connotations and become a common colloquial term used both by the public and police officers to refer to their profession.
First attested in English in the early 15th century, initially in a range of senses encompassing '(public) policy; state; public order', the word police comes from Middle Frenchpolice ('public order, administration, government'), in turn from Latin politia, which is the Latinisation of the Greek πολιτεία (politeia), "citizenship, administration, civil polity". This is derived from πόλις (polis), "city".