In most (not all) jurisdictions, a police officer in plain clothes is called a "detective".
They are simply called "Plain clothed police."
A plain clothes policeman is a law enforcement officer who does his job out of uniform. Plain clothes policemen are often a part of an undercover operation.
Detective
Slang term for a policeman (usually a constable)
A plain?
A plain that lies along a sea coast is called
It is called a plain.
plain
The largest plain in Europe is known as either the European Plain or the Great European Plain.
It is called a plain.
It is called a plain.
A coastal plain is what you call a plain that lies along a seacoast.