In some quarters, it's politically correct to call the Linux operating system the “GNU/Linux operating system.” The problem with “Linux” is that there is no completely correct way to name it because it was written by many different people in a vast, distributed development effort. Technically speaking, Linux is the name of the operating system's kernel, nothing more. The kernel is very important of course, since it makes the operating system go, but it's not enough to form a complete operating system.
Enter Richard Stallman, the genius-philosopher who founded the Free Software movement, started the Free Software Foundation, formed the GNU Project, wrote the first version of the GNU C Compiler (gcc), created the GNU General Public License (the GPL), etc., etc., etc. He insists that you call it “GNU/Linux” to properly reflect the contributions of the GNU Project. While the GNU Project predates the Linux kernel, and the project's contributions are extremely deserving of recog
nition, placing them in the name is unfair to everyone else who made significant
contributions. Besides, I think “Linux/GNU” would be more technically accurate
since the kernel boots first and everything else runs on top of it.
In popular usage, “Linux” refers to the kernel and all the other free and open source software found in the typical Linux distribution; that is, the entire Linux ecosystem, not just the GNU components.