Isthmus

Isthmus is a narrow strip of land connecting two larger land areas. It's sides are covered by water. Usually they obstruct the ocean navigation and canals are constructed to overcome them.

Some famous Isthmuses:

• The Isthmus of Kra connecting Malay Peninsula with the mainland of Asia.
• The Isthmus of Suez between North Africa and Sinai Peninsula. 
• Isthmus of Panama between North and South America. 
• Isthmus of Gibraltar