Quote Originally Posted by jshoer View Post
It's about 500 miles between our two nations, so my question for you is, what's an appropriate name for a 500-mile-wide strip of ocean between two roughly parallel coasts? Would it be a strait, a passage, or some other name I'm having trouble thinking of?
500 miles wide is definitely a sea - the Adriatic is only 100 miles at it's widest point, the Mediterrean not much more than 500 at its widest north-south distance. A strait is the narrow point between two larger bodies of water.

But really there's no hard and fast rules for any of these terms. The definition of a sea is a body of water enclosed by land, and an ocean is a body of water not enclosed by land... but all oceans are surrounded by land, and vice versa! Best not to worry about it too much.