Traditionally, in British and northern European usage, the Sound is the Oresund, the strait that separates Denmark (the Danish island of Sjaelland) and Sweden, the narrow channel (2.5 miles or 4 kilometers wide) that connects the Kattegat with the Baltic Sea.
There is little consistency in the use of 'sound' in English-speaking cartography.
In the United States, Long Island Sound separates Long Island from the coast of Connecticut, but on the Atlantic Ocean side of Long Island, the body of water between it and its barrier beaches is the Great South Bay. Pamlico Sound is a similar lagoon that lies between North Carolina and its barrier beaches, the Outer Banks, in a similar situation. On the West Coast, Puget Sound, by contrast, is a deep arm of the sea.
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