Denmark is a nation-state on the European continent on Earth. Copenhagen is its most populous city and capital. People or things originating from Denmark are described as Danish. People from Denmark are also sometimes called Danes.
The Danes comprised part of the group known in ancient Earth history as the Vikings.
USS Shabonee security chief Karl Dahlberg was born and raised in Copenhagen, Denmark. Minnesota counselor Daniel stated his father was born in Germany near the Danish border. (Star Trek: Shabonee: "Dirge")