A division of an ocean, delineated by landforms, currents (e.g. Sargasso Sea), or specific latitude or longitude boundaries. This includes but is not limited to marginal seas, and this is the definition used for inclusion in this list.
The World Ocean. For example, the Law of the Sea states that all of the World Ocean is "sea",[b] and this is also common usage for "the sea".
Any large body of water with "Sea" in the name, including lakes.
Strait - a narrow area of water connecting two wider areas of water
There are several terms used for bulges of ocean that result from indentations of land, which overlap in definition, and which are not consistently differentiated:
Bay - generic term; though most features with "Bay" in the name are small, some are very large
Gulf - a very large bay, often a top-level division of an ocean or sea
Fjord - a long bay with steep sides, typically formed by a glacier
Bight - a bay that is typically shallower than a sound
Sound - a large, wide bay which is typically deeper than a bight, or a strait
Many features could be considered to be more than one of these, and all of these terms are used in place names inconsistently; especially bays, gulfs, and bights, which can be very large or very small. This list includes large areas of water no matter the term used in the name.
Sources differ over which seas are considered marginal seas as well as which ocean a given sea is considered a marginal part of. There is no single ultimate authority on the matter.
^There is no accepted technical definition of sea among oceanographers. A rather weak definition is that a sea is a subdivision of an ocean, which means that it must have oceanic basin crust on its floor. This definition, for example, accepts the Caspian Sea, which was once part of an ancient ocean, as a sea. The Introduction to Marine Biology defines a sea as a "landlocked" body of water, adding that the term "sea" is only one of convenience, but the book is written by marine biologists, not oceanographers.The Glossary of Mapping Sciences similarly states that the boundaries between seas and other bodies of water are arbitrary.
^According to this definition, the Caspian would be excluded as it is legally an "international lake".
^ abcdefProposed names to the IHO 2002 draft. This draft was never approved by the IHO (or any other organization), and the 1953 IHO document (which does not contain these names which mostly originated from 1962 onward) remains currently in force. Leading geographic authorities and atlases do not use these names, including the 2014 10th edition World Atlas from the National Geographic Society and the 2014 12th edition of the Times Atlas of the World. But Soviet and Russian-issued state maps do include them.