Gulf's, sea's and bay's?

Question

What's the difference between a gulf, a sea, and a bay? What makes a gulf a gulf, a sea a seaand a bay a bay? And why isn't the "Hudson Bay," in Canada, or the "Sea of Okhostk," in Russia, considerded a gulf? Thanks to all.

Answer 1

Sea is an arm of an ocean. Through sea you can go onto the oceanic waters.

A gulf is a large body of sea-water hemmed in by two lands on either side.

A bay is an arm of a sea protruding into land that surrounds it on all sides except the one linking it to the wider sea. It is the counterpart of peninsula. Seas  or oceans have no counterpart of 'Island', as they are all connected as one global oceans and its arms.

However, these gradations are for a rough guidance, and are used interchangeably. The task of naming would have been much more accurate in these days of satellite pictures and google earth.    

Answer 2

(pssst: what yours all have in common is the apostrophe - it isn't needed for plural items)

I gotta' change my avatar to RedPen.