A peninsula is a landmass that is surrounded by water on three sides. The term "peninsula" is derived from the Latin words "paene" meaning "almost" and "insula" meaning "island". Peninsulas are formed when a narrow strip of land juts out into the sea or a large body of water. They can vary in size and shape, ranging from small and elongated to large and triangular.

Peninsulas are characterized by their unique geography, as they have a coastline on three sides. This makes them distinct from islands, which are completely surrounded by water. The presence of water on three sides of a peninsula provides a variety of natural advantages and challenges.

Advantages of Peninsulas:
1. Access to Water: Peninsulas offer easy access to water on multiple sides, making them ideal for activities such as fishing, trade, and transportation.
2. Natural Defense: The water surrounding a peninsula acts as a natural barrier, providing some level of protection against invasion or attacks from land.
3. Varied Landscapes: Peninsulas often feature diverse landscapes, including coastal areas, cliffs, beaches, and inland regions. This can create a unique and picturesque environment.

Challenges of Peninsulas:
1. Vulnerability to Storms and Erosion: Peninsulas are more exposed to the impact of storms and erosion due to their projection into the water. This can lead to coastal erosion and damage to infrastructure.
2. Limited Land Resources: Peninsulas have a limited amount of available land, especially if they are narrow or elongated. This can pose challenges for agriculture, urban development, and population growth.
3. Dependency on Water for Transportation: While water access can be advantageous, it also means that peninsulas are heavily dependent on water transportation for trade and connectivity. This reliance can be a disadvantage if there are issues with ports or maritime routes.

In conclusion, a landmass bounded by the sea on three sides is referred to as a peninsula. Peninsulas have distinct geographical characteristics and offer both advantages and challenges for the people and ecosystems that inhabit them.