First of All, What is Linux?
You see, there is a contradiction on what Linux really is. We see that people refer Linux as an Operating System but on the other hand, some people say that Linux is a kernel. Well, let’s put it this way.
In fact, Linux is a kernel written and named by Linus Torvalds which you can take a look from https://www.kernel.org/. When you think about it, kernel is a useless thingy if there is no software using it since kernel manages hardware based on software inputs.
At this point, we have a cute kernel with us.
On the other hand, Richard Stallman initiated GNU Project, aiming to create a free Operating System with free tools. They were pretty succesful with the mission but there was one thing missing. A proper kernel to manipulate hardware by these tools.
Now in addition to a kernel, we have these pretty GNU Project tools with us.
Both Linux and GNU Project were written with the same UNIX mindset therefore, both were compatible. Hence, they mixed Linux and GNU Project together and crafted this magnificent Full-Operating System called “GNU/Linux”.
But even this kind of bare Full-Operating System GNU/Linux was still not really useful since you couldn’t run applications you wanted such as Web Browser, E-mail etc.
To cut a long story short, today people often just use the name of the central kernel to refer to the whole system.
It is for you to decide what you call an “operating system”. Is it just the thing that manages hardware (like Linux) or is it the thing you interact with (like your favorite desktop environment), or maybe something in between like a basic (command line based) GNU/Linux.