A bay is a groove which is situated on coast of ground and which directly connects to a larger main body of water. It can join with an ocean, lake or another bay. A large bay has a lot of name such as a gulf, sea, sound, or bight. A cove is a type of smaller bay. It is an inlet with narrow entrance. A fjord is a particularly steep bay. Fjord is the result of glacial activity.

Bays can be the estuary of a river. For example, the Chesapeake Bay is an estuary of the Susquehanna River. Bays also can be situated within each other. For example, James Bay is an arm of Hudson Bay in northeastern Canada. Some large bays, such as the Bay of Bengal and the Hudson Bay, have varied marine geology.

The land surrounding a bay is a very save and quite place from strength of winds and it blocks waves. First of all, it provided a safe place for fishing. Also they were so important for people that they were used for trade and gave had a lot of place for becoming a ports.

The United Nations Convention on the Law of the Sea (UNCLOS), also called the Law of the Sea defines a bay as a well-marked indentation whose penetration is in such proportion to the width of its mouth as to contain land-locked waters and constitute more than a mere curvature of the coast. An indentation shall not, however, be regarded as a bay unless its area is as large as, or larger than, that of the semi-circle whose diameter is a line drawn across the mouth of that indentation.

There are multiple ways from which bays can be created. The largest bays are the result of plate tectonics. As the super-continent Pangaea split up along curved and indented fault lines, the continents moved apart and the world’s largest bays formed. These include the Gulf of Guinea, Gulf of Mexico and the Bay of Bengal. The last one is the largest bay in the world.

Glacial and river erosion are other ways why bays formed. Rias are created by rivers and are characterized by more gradual slopes. Currents can make waves more constant, and soft rocks speed erosion. The Gulf of California is an example of a bay created by plate tectonics as Baja California peninsula moves away from the Mexican mainland.