No, Japan is not a peninsula. Japan is an archipelago, which means it is a chain of islands. The country is made up of four main islands: Honshu, Hokkaido, Kyushu, and Shikoku, along with thousands of smaller islands. These islands are located in the Pacific Ocean, off the eastern coast of Asia.
A peninsula, on the other hand, is a piece of land that is almost entirely surrounded by water but is connected to a larger landmass. Examples of peninsulas include the Korean Peninsula and the Iberian Peninsula. Since Japan is not connected to any larger landmass and is entirely surrounded by water, it does not qualify as a peninsula.