A paramilitary is a semi-militarized force whose organizational structure, tactics, training, subculture, and (often) function are similar to those of a professional military, but which is not included as part of a state's formal armed forces.
Under the law of war, a state may incorporate a paramilitary organization or armed agency (such as a national police, a private volunteer militia) into its combatant armed forces. The other parties to a conflict have to be notified thereof.
The use of the term paramilitary can be debated, but the general consensus being of a combatant force or organization, more military-like than civilian. Organizations that have been described as paramilitary are as diverse as the Minutemen, Black Panthers, SS, youth groups (from scouting to the Pioneer movement), and even military-themed boarding schools.
Though a paramilitary is not a military force, it is usually equivalent to a military's light infantry force in terms of intensity, firepower, and organizational structure. A paramilitary may also commonly fall under the command of a military, even despite not being part of the military or play an assisting role for the military in times of war.
Types
Depending on the standards used, "paramilitaries" may include:
Irregular military forces: militias, guerrillas, insurgents, terrorists, and so forth
The auxiliary forces of a state's military: National Guard, Presidential Guard, Republican Guard, State Guard
Some kinds of police forces, such as auxiliary police
Gendarmeries, such as Egyptian Central Security Forces and Russia's National Guard
Border guards, such as Russia's Border Guard Service
The United States' Federal Protective Forces,
Security forces of ambiguous military status: internal troops, railroad guards or railway troops
Semi-militarized law enforcement personnel, such as SWAT teams in the United States and a number of other countries
Foreign volunteers
Youth Military Cadet Organisations, such as Junior Reserve Officers' Training Corps, Bangladesh National Cadet Corps
In the United Kingdom and Ireland, the term is often restricted to the various armed groups involved in the Northern Ireland Troubles, such as the Ulster Volunteer Force or the Provisional Irish Republican Army.