The "sea" or the "ocean" are words used to describe all the interconnected salt waters of the world including the five great oceans (see our oceans page for more).

In geographic terms (and for this page), "sea" is used in the name of specific, smaller bodies of seawater. Seas of the world usually make up partly landlocked areas within the much larger five great oceans.

Seas only partially landlocked and/or bounded by submarine ridges on the sea floor are often referred too as marginal seas. Opinions often differ over which seas are considered marginal seas, some are found within mediterranean seas.

Marginal seas of the Arctic Ocean include: Barents Sea, Beaufort Sea, Chukchi Sea, Kara Sea and Laptev Sea.

Some marginal seas of the Southern Ocean include: Amundsen Sea, Ross Sea, and Weddell Sea.

Some marginal seas of the Atlantic Ocean include: the Argentine Sea, English Channel, Gulf of Mexico, Hudson Bay, Irish Sea, North Sea, and Norwegian Sea.

Indian Ocean marginal seas include: Andaman Sea, Arabian Sea, Bay of Bengal.

Pacific Ocean marginal seas include: the Bering Sea, Celebes Sea, Coral Sea, East and South China Seas, Philippine Sea, Japan Sea, Sea of Okhotsk, Tasman Sea and the Yellow Sea.

A mediterranean sea, is a sea that is nearly completely enclosed by land and therefore has a very limited exchange of water with the outer oceans. Water circulation within these seas is often dependent on changed salinity (salt content) and temperature levels rather than open ocean trade winds and currents.

There are two types of mediterranean seas: concentration basins, dilution basins.

A concentration basin has a higher salinity (salt) level than the open oceans due to evaporation. The upper layer of water is an inflow of fresh oceanic water and the bottom layer of water is out flowing saltier water.

A dilution basin has a lower level of salinity (salt) due to the amount of freshwater that enters the sea from rainfall and via rivers. Water at the top is fresher and it flows out of the sea, while at deeper depths saltier oceanic water flows in.

Confusingly, the Mediterranean Sea is a type of mediterranean sea and within it are marginal seas such as: the Adriatic Sea, Aegean Sea, Alboran Sea, Balearic Sea, Ionian Sea, Ligurian Sea, and the Tyrrhenian Sea.

In the Atlantic Ocean, the American Mediterranean Sea is the combination of the marginal seas of the Gulf of Mexico and the Caribbean Sea.

Mediterranean seas of the Indian Ocean include: Persian Gulf and the Red Sea.

The Australasian Mediterranean Sea includes the marginal seas of the Banda Sea, the Sulu Sea, the Sulawesi Sea and the Java Sea.

Some fully landlocked (inland) salt waters are often called seas, but these water bodies are in fact saltwater lakes or hypersaline lakes. Examples of inland saltwater seas include the Caspian Sea and the Dead Sea.

Brackish seas are waters that have higher levels of salinity than freshwater but lower levels than seawater, including the Baltic Sea, the Black Sea and the Caspian Sea (technically an inland saltwater lake).