Trooper is a rank used by several civilian police forces in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. In its plural form, troopers, it generally refers to members of state highway patrol

Highway patrol

A highway patrol is either a police unit created primarily for the purpose of overseeing and enforcing traffic safety compliance on roads and highways, or a detail within an existing local or regional police agency that is primarily concerned with such duties.Duties of highway patrols or traffic...

 or state police

State police

State police are a type of sub-national territorial police force, particularly in Australia and the United States. Some other countries have analogous police forces, such as the provincial police in some Canadian provinces, while in other places, the same responsibilities are held by national...

 agencies, even though those officers may not necessarily be of the rank of trooper.

For example, in the Louisiana State Police

Louisiana State Police

The Louisiana State Police is the state police department of Louisiana, which has jurisdiction anywhere in the state, headquartered in Baton Rouge. It was created to protect the lives, property and constitutional rights of people in Louisiana. It falls under the authority of the Louisiana...

, Trooper is a rank below Trooper First Class

Trooper First Class

Trooper first class is a rank used by several state police agencies within the United States and in some world militaries.In particular, in the Louisiana State Police, it is a rank below senior trooper, yet above trooper. The insignia for this rank consists of a gold colored 'TFC' collar pin worn...

, and above Cadet

Cadet

A cadet is a trainee to become an officer in the military, often a person who is a junior trainee. The term comes from the term "cadet" for younger sons of a noble family.- Military context :...

. The insignia for this rank consists of a gold colored 'TPR' collar pin worn on the wearer's right lapel. Cadets who complete the state police academy are automatically promoted to Trooper. The title of address is "Trooper".

Early Australian police forces had officers termed troopers, typically mounted police

Mounted police

Mounted police are police who patrol on horseback or camelback. They continue to serve in remote areas and in metropolitan areas where their day-to-day function may be picturesque or ceremonial, but they are also employed in crowd control because of their mobile mass and height advantage and...

. For example, the classic Australian folk song Waltzing Matilda

Waltzing Matilda

"Waltzing Matilda" is Australia's most widely known bush ballad. A country folk song, the song has been referred to as "the unofficial national anthem of Australia"....

 contains the line "Down came the troopers, one, two, three," referring to three mounted police who had come to arrest the swagman

Swagman

A swagman is an old Australian and New Zealand term describing an underclass of transient temporary workers, who travelled by foot from farm to farm carrying the traditional swag...

. The term is no longer in common usage in Australia.

Usage in other agencies or countries may vary.