We'll begin with the different forms of flowing water. The smallest water channels are often called brooks but creeks are often larger than brooks but may either be permanent or intermittent. Creeks are also sometimes known as streams but the word stream is quite a generic term for any body of flowing water. Streams can be intermittent or permanent and can be on the surface of the earth, underground, or even within an ocean (such as the Gulf Stream).
A river is a large stream that flows over land. It is often a perennial water body and usually flows in a specific channel, with a considerable volume of water. The world's shortest river, the D River, in Oregon, is only 120 feet long and connects Devil's Lake directly to the Pacific Ocean.
A pond is a small lake, most often in a natural depression. Like a stream, the word lake is quite a generic term - it refers to any accumulation of water surrounded by land - although it is often of a considerable size. A very large lake that contains salt water, is known as a sea (except the Sea of Galilee, which is actually a freshwater lake).
A sea can also be attached to, or even part of, an ocean. For example, the Caspian Sea is a large saline lake surrounded by land, the Mediterranean Sea is attached to the Atlantic Ocean, and the Sargasso Sea is a portion of the Atlantic Ocean, surrounded by water.
Oceans are the ultimate bodies of water and refers to the five oceans - Atlantic, Pacific, Arctic, Indian, and Southern. The equator divides the Atlantic Ocean and Pacific Oceans into the North and South Atlantic Ocean and the North and South Pacific Ocean.
Coves are the smallest indentations of land by a lake, sea, or ocean. A bay is larger than a cove and can refer to any wide indentation of the land. Larger than a bay is a gulf which is usually a deep cut of the land, such as the Persian Gulf or the Gulf of California. Bays and gulfs can also be known as inlets.
Any lake or pond directly connected to a larger body of water can be called a lagoon and a channel explains a narrow sea between two land masses, such as the English Channel.