An «island» is a piece of land surrounded by water on all sides — whether that water is a sea, an ocean, or even a large river or lake. Islands vary greatly in size: some are so small you can walk around them in minutes, while others are huge, like «Greenland», the largest island in the world.
There are also groups of nearby islands called an «archipelago», like the many islands of Indonesia, numbering over seventeen thousand. Some islands form from underwater volcanic eruptions, while others are built from coral reefs.
Islands are sometimes home to unique animals and plants found nowhere else, because being cut off from the mainland lets them develop in special ways — as seen on the famous Galápagos Islands.
