A doorway made of water
A strait is a narrow passage of water connecting two larger bodies of water. Picture two stretches of sea joined by a watery doorway, with land on either side.
Merriam-Webster’s geographical definition gives the key clue: the passage connects water to water. Its size on a map can hide how useful that little gap is.
Gibraltar joins two blue spaces
The Strait of Gibraltar connects the Atlantic Ocean and the Mediterranean Sea. Spain lies on one side; Morocco lies on the other.
NASA’s astronaut photograph of Gibraltar shows the passage between Europe and Africa. Follow the water through the gap and you can see why a strait is a connection, not a dead end.
Waterway or land bridge?
A strait and an isthmus can look like opposite answers to the same puzzle. A strait is water between areas of land. An isthmus is land between areas of water, joining two larger land areas.
One lets you follow a water route; the other gives you a land connection.
Let your eye follow the gap
Next time a map looks like a jumble of coastlines, trace the blue part first. Does a narrow passage open into a larger body of water at each end?
That is the useful picture to remember: two wide blue spaces, one narrow watery doorway.