I have found that many users of GNU/Linux often mistake the Linux kernel for the whole GNU free software spectrum. Let me clear things up for people.
In 1983 Richard M. Stallman (or RMS), at the Massachusetts Institute of Technology (or MIT) was majorly hacked off with the advent of proprietary closed-source software, and decided to trigger off a completely new operating system consisting of totally free software that respects the user's right to view the source code, copy the code, edit the copy and then redistribute the copy whilst letting the users of the copy redistribute and install the new operating system onto as many computers as they wish. This operating system was called "GNU"; many would think of that animal from Africa but is actually an anogram for "GNU is Not Unix" because this operating system may act like Unix but really it is not. This operating system was going pretty well for RMS and the newly-founded Free Software Foundation, but they lacked an important piece, the last piece: the kernel. It was not until 1991 when Linus Torvalds, a computer science student at the University of Helsinki, created the Linux kernel to install the last piece into the new GNU Operating System.
Although there is only one GNU Operating System. Many computer programmers have followed the idea and created many GNU/Linux operating systems (e.g. Ubuntu) but because it does not consist of totally free software and web applications, it cannot be labelled "Free software" but is named "Open Source" instead. Remember that when you use a Linux operating system, you are not; there is no such thing as a Linux operating system as it is only the kernel - a component of the GNU/Linux operating system.
I am writing this message using GNU/Linux right now. I hope I have cleared things up.