In geography a sound is a large sea or ocean inlet larger than a bay, deeper than a bight, wider than a fjord, or it may identify a narrow sea or ocean channel between two bodies of land (see also strait).

There is little consistency in the use of 'sound' in English-speaking cartography.

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.

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.

A Sound is often formed by the sea flooding a river valley. This produces a long inlet where the sloping valley hillsides decend to sea-level and continue beneath the water to form a sloping sea floor. The Marlborough Sounds in New Zealand are a good example of this type of formation.

Sometimes a Sound is produced by a glacier carving out a valley on the coast then receding, or the sea invading a glacier valley. The glacier produces a sound that often has steep, near vertical, sides that extend deep under water. The sea floor is often flat and deeper at the landward end than the seaward end, due to glacial deposits. This type of sound is more properly termed a fjord (or fiord). The sounds in Fiordland, New Zealand, have been formed this way.