>>717407376Gulf is mostly surrounded by land, directly leads into the ocean salt water, typically at the end of a major river. A very large area covered.
Lagoon is entirely separated from the ocean by a very thin amount of land, brackish water
Bay is ocean mostly surrounded by land, smaller total surface area than a gulf but typically a larger opening for easier access.
Sound is an inlet, a narrow (but not the most narrow) straight between two landmasses as the result of ocean water entering some kind of depressed area. Typically separates an island from the mainland.