What is Linux?

According to Linux.com, Linux is a modern operating system. This means that it runs on 32-bit and 64-bit architectures, uses preemptive multitasking, protected memory, supports multiple users, and has rich support for networking, including TCP/IP networking. Linux was originally written for Intel's 386 architecture, but now runs on a wide variety of hardware, including the full x86 family of processors, as well as Alpha, SPARC, and of course PowerPC chips.

Actually it is rather difficult to answer to the question because Linux is just more than a kernel or an operating system, it's a whole experience. That's why I think the answer can be given better by answering to the following questions:

Why should someone use Linux?
What does it do?
Where can I get it?
What does it look like?