The Bay of Biscay is a gulf

Bay

A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...

 of the northeast Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 located south of the Celtic Sea

Celtic Sea

The Celtic Sea is the area of the Atlantic Ocean off the south coast of Ireland bounded to the east by Saint George's Channel; other limits include the Bristol Channel, the English Channel, and the Bay of Biscay, as well as adjacent portions of Wales, Cornwall, Devon, and Brittany...

. It lies along the western coast of France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 from Brest

Brest, France

Brest is a city in the Finistère department in Brittany in northwestern France. Located in a sheltered position not far from the western tip of the Breton peninsula, and the western extremity of metropolitan France, Brest is an important harbour and the second French military port after Toulon...

 south to the Spanish

Spain

Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...

 border, and the northern coast of Spain west to Cape Ortegal, and is named in English after the province of Biscay

Biscay

Biscay is a province of Spain and a historical territory of the Basque Country, heir of the ancient Lord of Biscay. Its capital city is Bilbao...

, in the Spanish Basque Country

Basque Country (autonomous community)

The Basque Country is an autonomous community of northern Spain. It includes the Basque provinces of Álava, Biscay and Gipuzkoa, also called Historical Territories....

.

The average depth is 1744 metres (5,721.8 ft) and maximum depth is 2789 metres (9,150.3 ft).
Parts of the continental shelf

Continental shelf

The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...

 extend far into the bay, resulting in fairly shallow water in many areas and thus cause the rough seas for which the region is known.