The Darién Gap is the narrow strip of land that connects Panama (part of Central America) to Colombia (part of South America). While not an isthmus in the traditional sense, it is the physical connection between the two continents.

Here's why it's not technically an isthmus:

* Isthmus usually refers to a narrow strip of land connecting two larger landmasses, typically with a body of water on either side.

* The Darién Gap is mostly dense rainforest and marshland, making it difficult to traverse.

* There is no major body of water separating Panama and Colombia, so it doesn't fit the typical definition of an isthmus.

However, it is still the only land bridge connecting North and South America.