Many people use the term "Linux" to refer to entire LinuxDistributions, which include not only the Kernel but also the many programs such as the GNU shell, C Library, and toolchain that are needed to create and run other programs. There are many (literally thousands of) different flavours of LinuxDistributions. See Category:Distribution for a list of LinuxDistributions we care about, or visit http://www.distrowatch.com/. The LinuxFaq might also be of help.
RMS insists that these be referred to as GNU/Linux distributions, on grounds that the Kernel is exchangeable. While these GNU systems run on top of the LinuxKernel, you might also use the Hurd Kernel, which you should then refer to as a "GNU/Hurd" system. In practice, this terminology has not caught on much.
Check out the WellThoughtOutReasonsToRunLinux.
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