A large but narrow part of ocean which invades farther inland is called gulf.
Textbook answer: Gulf is a portion of the sea, that is almost surrounded by land except one narrow opening.
They are formed when a piece of land sinks for whatever reason. This causes a huge indentation in the area. When water fills it up a gulf is formed.
Gulfs are also formed through a natural process of erosion. Erosion is caused by water or wind beating away at a surface over a period of time. All this doesn’t happen overnight. It takes a long, long time, sometimes millions of years.
Gulfs are generally named after the countries or cities that surround them. While there are many gulfs found all over the world, there are a few that are hugely popular.
Let's look at the largest and the most politically and economically important gulfs.
The Gulf of Mexico is the largest gulf in the world. It was formed approximately 300 million years ago when a seafloor sank. It is located on the coast of Mexico and The United States of America. It is an extension of Atlantic Ocean. The United States gets much of its seafood from here.
Persian gulf is politically and economically important. It is hemmed in by Iran, Iraq, Bahrain, Kuwait, Qatar, Saudi Arabia and the United Arab Emirates. It is an extension of Arabian Sea. Most of the world’s oil is shipped through the Persian Gulf to other parts of the world.