You have waves in the ocean which exists, we have to we have to understand how the waves are defined. Because if we do not define the waves, we cannot go to the next step up, when we put a ship in the waves how is the ship behaves. So, first of all we have to understand how typically wave is defined. This is what we will be doing the rest of the class today. That is we are studying what is called regular sea waves. I will explain the term why we say regular sea wave later on.