When you go to an automotive or boating store, you will see many different types of oil. To me, all those numbers, names, and phrases mean essentially nothing. They are all confusing and complicated. What I basically understand is that there are different types of oil for different types of engines. Car engines differ from boat motors, so they use different oil.
For example, 2 stroke oil is a type of engine oil that is used for two stroke engines. Engines that require this type of oil are generally small motors, like the kind that you would find in your lawn mower. The oil is added directly to the gasoline, rather than in some special tank. This means that the oil will be consumed in the same way that gasoline is.