Linux
Linux is a free operating system created by Linus Torvalds. It is, according to Wikipedia, "a Unix-like computer operating system ... one of the most prominent examples of free software." That is to say, Linux is a completely free piece of software capable of running a computer. Some people tend to think Linux is a program that runs on Microsoft's Windows or another version of Windows. It is not. It is an operating system totally independent of Microsoft and Windows or any other operating system, for that matter. The name Linux, originally GNU/Linux, comes from the name of its creator, Linus Torvalds, and from Unix. The prefix GNU is the name of the company which created the original utilities which allowed people to actually make use of Linux. GNU also created the GPL, which is the license which Linux is released under. The GPL basically states that you may change and redistribute the software as long as you give credit where it is due. It has become common-place to drop the GNU off the front of the name, shortening it to just Linux. Linux has become the standard for Internet servers of all sorts and sizes. It is also gaining ground on the desktop market.