Peninsulas:-

Landmasses that are surrounded by the sea on three sides and connected to the mainland on the fourth side are called Peninsulas.

ex: Italy is a peninsula. Norway and Sweden are also a part of the peninsula, known as Scandinavian Peninsula.

Bays & Gulfs:-

Bays and gulfs are parts of the sea enclosed by land on three sides. In a  bay, the land curves inwards and the mouth of the bay is usually wide as in the case of Bay of Bengal.

A gulf is a narrow inlet of the sea and has a narrow mouth. The entire Baltic Sea is a large gulf. 



Importance of Bays and Gulfs:

Since the bays and gulfs are protected from the storms of the high seas, they are very useful for building harbors where ships can be safely anchored and cargo can be loaded or unloaded.