Isthmus

: isthmuses or isthmi)[2] is a narrow piece of land connecting two larger areas across an expanse of water by which they are otherwise separated.

[3] A tombolo is an isthmus that consists of a spit or bar, and a strait is the sea counterpart of an isthmus, a narrow stretch of sea between two landmasses that connects two larger bodies of water.

The term land bridge is usually used in biogeology to describe land connections that used to exist between continents at various times and were important for the migration of people and various species of animals and plants, e.g. Beringia and Doggerland.

[4] An isthmus is a land connection between two bigger landmasses, while a peninsula is rather a land protrusion that is connected to a bigger landmass on one side only and surrounded by water on all other sides.

Canals are often built across isthmuses, where they may be a particularly advantageous shortcut for marine transport.