The Mozambique Channel is the channel of the Indian Ocean between the island of Madagascar and the mainland of Africa (specifically the country of Mozambique, hence the name). It's about 1,000 miles (1,600 km) long, 10,000 feet (3,000 m) deep at its deepest, and varies from 250 to 600 miles (400 to 950 km) wide; this was wide enough that Madagascar was not settled by humans until somewhere between 200 and 500 A.D., and people of Indonesian descent probably traveled across the Indian Ocean to Madagascar before or about the same time as people coming directly from Africa.
The Comoros archipelago and the island of Mayotte are at the north end of the channel, and inside it are Juan de Nova island and Bassas da India. Several of these islands are claimed both by Madagascar and its former colonist, France. These uninhabited islands are of strategic importance because of the large amount of shipping that goes through the channel, both for short trips along the African coast and longer-distance hauls around the Cape of Good Hope. During World War II, Madagascar was still controlled by German-dominated Vichy France, and the Allies thought that Japanese use of its ports was a serious enough threat to mount an amphibious attack, "Operation Ironclad," on the island with ships and submarines from the north end of the channel.
All the major rivers of Madagascar empty into the channel, as well as the Zambezi and Limpopo Rivers on the mainland. The major current is the warm Mozambique Current, which flows southwestward; the warm water may be why some of the Southern Hemisphere's severest cyclones originate here.