The smallest ocean is the Arctic Ocean with the North Pole in the centre. This ocean is connected to the Pacific and Atlantic Oceans via small gaps between continents
Seas.Small and large parts of ocean that are divided by land, islands or underwater uplands are called seas. The largest seas are the Philippine Sea, the Coral Sea, the Arabian Sea, the South China Sea, the Caribbean Sea and others.
Gulf is a component of oceans, seas, lakes, which juts out the land, but has free exchange with their major parts. For example: the Persian Gulf, the Gulf of Mexico, the Gulf of Alaska etc.
Channel is rather narrow space, which connect water area with any separate land’s parts. Canal – man-made basin. (Suez, Panama Canals)