A peninsula is a piece of land that sticks out into water, surrounded by water on three sides but still connected to the mainland on one side.

Think of a peninsula like a finger reaching into a lake or ocean. Florida is a famous peninsula, jutting southward into the Atlantic Ocean and the Gulf of Mexico while remaining attached to the rest of the United States. Italy is a boot-shaped peninsula extending into the Mediterranean Sea. The Korean Peninsula connects to mainland Asia in the north but is surrounded by water on its other three sides.

Peninsulas can be any size, from massive landmasses like Arabia to small pieces of land at your local lake. Some peninsulas are so narrow where they connect to the mainland that they almost look like islands. The connecting strip of land is sometimes called an isthmus.

Throughout history, peninsulas have been strategically important because they're easier to defend (water on three sides makes it harder for armies to attack) and excellent for trade (access to the sea on multiple coastlines). Ancient Greece developed on a mountainous peninsula, and its access to the sea helped Greek culture spread across the Mediterranean world.