Explanation The word peninsula has its origins from the Latin words pene meaning 'almost', followed by insula referring to an 'island'. When merged, 'pene' and 'insula' form the word peninsula; a landform that appears like an island, but actually isn't considered as one. The Arabian Peninsula is a perfect example of such a landform type. Other examples include the Kenai Peninsula of Alaska in USA, or Baja Peninsula in Mexico. Formation The tectonic plates of the Earth's lithosphere comprise land masses over them. These masses are highly affected by occurrences within the Earth's core, thereby leading to shifting, pushing, rising, or sinking. Thus, one of the main reasons behind the formation of peninsulas are the gradual lithospheric activities. On the other hand, rising water levels may contribute to the formation of peninsulas. The world is aware of rising temperatures, melting glaciers, tropical storms, etc., that add to the rise of water levels. Due to this, many land masses become surrounded by water on sides, forming a peninsula, in case of three sides. Soil erosion is known to form these landforms to a significant extent. Weathering agents erode the soil, making the landmass vulnerable to be submerged by water. This results in formation of a peninsula, or an island, in specific conditions. Difference between a Bay and a Peninsula A bay is a water-body surrounded by land on three sides. For peninsula, it's the other way round. Peninsula is a land mass, surrounded by water on three sides. For example, the Bay of Bengal forming the north-eastern part of the Indian Ocean or San Sebastian Bay in Spain. Both of them are surrounded by land on three sides.