So, some time ago Richard Stallman said this:

I’d just like to interject for a moment. What you’re referring to as Linux, is in fact, GNU/Linux, or as I’ve recently taken to calling it, GNU plus Linux. Linux is not an operating system unto itself, but rather another free component of a fully functioning GNU system made useful by the GNU corelibs, shell utilities and vital system components comprising a full OS as defined by POSIX. Many computer users run a modified version of the GNU system every day, without realizing it. Through a peculiar turn of events, the version of GNU which is widely used today is often called “Linux”, and many of its users are not aware that it is basically the GNU system, developed by the GNU Project. There really is a Linux, and these people are using it, but it is just a part of the system they use. Linux is the kernel: the program in the system that allocates the machine’s resources to the other programs that you run. The kernel is an essential part of an operating system, but useless by itself; it can only function in the context of a complete operating system. Linux is normally used in combination with the GNU operating system: the whole system is basically GNU with Linux added, or GNU/Linux. All the so-called “Linux” distributions are really distributions of GNU/Linux.

and it became a joke. Of course its not completely false - GNU utils do play a big role in the Linux ecosystem but they are not as important as they used to be so the proposed name GNU/Linux was a bit of a exaggeration. But I’ve never found a cool answer to this until recently - here it is.

I’m terribly sorry for interjecting another moment, but what I just told you is GNU/Linux is, in fact, just Linux, or as I’ve just now taken to calling it, Just Linux. Linux apparently does happen to be a whole operating system unto itself and comprises a full OS as defined by POSIX.

Most computer users who run the entire Linux operating system every day already realize it. Through a peculiar turn of events, I was misled into calling the system “GNU/Linux”, and until now, I was unaware that it is basically the Linux system, developed by the Linux project.

There really isn’t a GNU/Linux, and I really wasn’t using it; it is an extraneous misrepresentation of the system that’s being used. Linux is the operating system: the entire system made useful by its included corelibs, shell utilities, and other vital system components. The kernel is already an integral part of the Linux operating system, never confined useless by itself; it functions coherently within the context of the complete Linux operating system. Linux is never used in combination with GNU accessories: the whole system is basically Linux without any GNU added, or Just Linux. All the so-called “GNU/Linux” distributions are really distributions of Linux.

Please keep in mind that I do respect him. I also mostly agree on his words and ideas, but sometimes he gets off track.