For the end user
, Linux, generally speaking, is an operating system much like Windows and the OSX on Mac. the difference is that there are many different flavours of it. Think of it as coffee. You can have decaf or put ice in it, but at the end of the day it does the same thing. Linux can do pretty much anything Windows can do, and often much, much more. It's free to use by anyone. Plus there are no problems like viruses or worms like as in the windows world, and linux is much safer otherwise too. It runs firefox and chrome, you can edit audio, video and do 2D and 3D animation. You can convert media files, upload them to servers on the internet, or run your own server. Linux is completely configurable. Chances are, you've got Linux in your pocket too. Android runs Linux, so you already use it. Linux will give you better battery backup on your laptop, run flawlessly on your aging desktop PC, or run securely on your server. Anything you want to do, you can do it on Linux.
Plus it can "do infinite loops in five seconds."
Download a flavour of Linux here
EDIT: The simplicity is for the noob. Poeple from the world of windows (WoW! don't often know what a kernel is. I for one can't explain operating system design in one BB post