Many computer old-timers love UNIX and its command line interface. But all those commands are not easy to remember for newcomers. X-Windows is a graphical interface for UNIX that some think is even easier to work with than Windows 98. Linux is an operating system similar to UNIX that is becoming more and more popular. It is a open-source program created by Linus Torvalds at the University of Finland, starting in 1991.
Open source means that the underlying computer code is freely available to everyone.
Programmers can work directly with the code and add features. They can sell their customized version of Linux, as long as the source code is still open to others. You can find more info at the Linux home site. By the way, the word Linux is generally pronounced with a short i and the accent on the first syllable, like LIH-nucks. Here is a link to an audio file of Linus Torvalds pronouncing it in English.