What feature is typically used to define a peninsula?

A peninsula is defined as a landmass that is surrounded by water on three sides. This geographical feature often extends into a body of water, which can be an ocean, sea, lake, or river. The defining characteristic of a peninsula is its partial encirclement by water, which differentiates it from islands, which are completely surrounded by water.

In the context of the choices provided, options describing a landmass surrounded by water on one side or two sides do not capture the essence of a peninsula, as they refer to various other geographical forms such as bays or capes. A landmass surrounded by water on all sides constitutes an island, not a peninsula. The distinction is important in geography, as it helps in classifying landforms and understanding their impact on human activity, ecosystems, and navigation routes.