Explanation:
A landmass bounded by the sea on three sides is referred to as a peninsula. The word peninsula comes from the Latin words "paene" meaning almost and "insula" meaning island. A peninsula is a landform surrounded by water on three sides and connected to a mainland on one side. Peninsulas are formed by various geological processes, such as erosion, submergence of land, and volcanic activity.

Characteristics of a Peninsula:
Some of the key characteristics of a peninsula are:

1. Surrounded by water on three sides: A peninsula is a landform that is surrounded by water on three sides. This means that it is connected to a larger landmass on one side.

2. Diverse geography: Peninsulas can have diverse geography, including mountains, hills, valleys, plains, and coastal areas.

3. Rich biodiversity: Due to their varied geography, peninsulas often have a rich biodiversity. They are home to numerous plant and animal species, including many that are endemic to the region.

4. Strategic location: Due to their location, peninsulas have often been strategic locations for trade, military, and political purposes.

Examples of Peninsulas:
Some of the well-known peninsulas in the world are:

1. Arabian Peninsula: The Arabian Peninsula is located in Southwest Asia and is surrounded by the Red Sea, the Persian Gulf, and the Arabian Sea.

2. Balkan Peninsula: The Balkan Peninsula is located in Southeast Europe and is surrounded by the Adriatic Sea, the Aegean Sea, and the Black Sea.

3. Iberian Peninsula: The Iberian Peninsula is located in Southwest Europe and is surrounded by the Atlantic Ocean and the Mediterranean Sea.

4. Indian Peninsula: The Indian Peninsula is located in South Asia and is surrounded by the Bay of Bengal, the Arabian Sea, and the Indian Ocean.

Conclusion:
In conclusion, a landmass bounded by the sea on three sides is known as a peninsula. Peninsulas have diverse geography, rich biodiversity, and are often strategic locations for trade, military, and political purposes. Some of the well-known peninsulas in the world are the Arabian Peninsula, the Balkan Peninsula, the Iberian Peninsula, and the Indian Peninsula.