What is Bay?

Legal Definition
A bay is a body of water connected to an ocean or lake, formed by an indentation of the shoreline. A large bay may be called a gulf, a sea, a sound, or a bight. A cove is a smaller circular or oval coastal inlet with a narrow entrance; some coves may be referred to as bays. A fjord is a particularly steep bay shaped by glacial activity.

Bays can exist as the estuary of a river, as the estuary of the Parramatta River in Australia. Bays may be nested in each other; for example, James Bay is an arm of Hudson Bay. Some large bays, such as the Bay of Bengal and the Hudson Bay, have varied marine geology.

The land surrounding a bay can often block waves and reduce the strength of winds. Thus bays were significant in the history of human settlement because they could provide a safe place for fishing. Later they were important in the development of sea trade as the safe anchorage they provide encouraged their selection as ports.
-- Wikipedia
Legal Definition
Is an enclosure to keep in the water for the supply of a mill or other contrivance, so that the water may be able to, drive the wheels of such mill. Stat. 27 Eliz. c. 19.

2. A large open water or harbor where ships may ride, is also called a bay; as, the Chesapeake Bay, the, Bay of New York.
-- Bouviers Law Dictionary
Legal Definition
A pond-head made of a great height to keep in water for the supply of a mill, etc., so that the wheel of the mill may be turned by the water rushing thence, through a passage or flood-gate. St. 27 Eliz. c. 19. Also an arm of the sea surrounded by land except at the entrance. In admiralty law and marine insurance. A bending or curving of the shore of the sea or of a lake. State v. Gilmanton, 14 N. H. 477. An opening into the land, where the water Is shut in on all sides except at the entrance. U. S. v. Morel, 13 Amer. Jur. 286, Fed. Cas. No. 15,807.
-- Black's Law Dictionary
Legal Definition
A mill-pond.
-- Ballentine's Law Dictionary