The Cantabrian Sea is the coastal sea of the Atlantic Ocean that washes the northern coast of Spain and the southwest side of the Atlantic coast of France; it represents the south area of the Bay of Biscay. It extends from the cape Estaca de Bares in the province of Corunna, to the mouth of the Adour river, near the city of Bayonne on the coast of the department of Pyrenees Atlantiques in French Basque Country. It washes 800 kilometers of coastline shared by the provinces of Corunna, Lugo, Asturias, Cantabria,  Vizcaya and Guipúzcoa and Labourd.

The Bay of Biscay (, ) is a gulf of the northeast Atlantic Ocean located south of the Celtic Sea. It lies along the western coast of France from Brest south to the Spanish border, and the northern coast of Spain west to Cape Ortegal.