Linux (pronounced LINN-ux) is a family of open-source operating systems, which means they can be modified and distributed by anyone around the world. This is different from proprietary software like Windows, which can only be modified by the company that owns it (Microsoft). The advantages of Linux are that it is free, and there are many different distributions (or versions) you can choose from. Each distribution has a different look and feel, and the most popular ones include Ubuntu, Mint, and Fedora.
Linux is named after Linus Torvalds, who created the Linux kernel in 1991. The kernel is the computer code that is the central part of an operating system.
According to StatCounter Global Stats, Linux users account for less than 1% of the operating systems market as of January 2013. However, most servers run Linux because it's relatively easy to customize.