Most people look at Distros like Ubuntu and Fedora and Slackware and call them “Linux”. When these distros boot up and get into a GUI environment, people call the GUI linux as well.
But…..That is not true!
Linux is actually just the kernel. The Linux kernel talks to the hardware in your computer and gets it to perform tasks based on your instructions, which are passed to the kernel via the command interpreter, also known as the “shell” or via applications that talk directly to the kernel. The kernel handles things like memory allocations, I/O operations, device management, file management and process management. It is in essence, the heart of the operating system.
So now that we have established that linux actually refers to the kernel, what are all the other things on your Distro? what handles the GUI? where are the panels and menus from? what gives you the cool desktop effects? The answer is that they are all seperate programs and on most linux distributions, these programs are all free and open-source meaning that everybody who understands programming can simply download the programming code and modify the program to suit their needs. So when you boot up your distro and look at the user interface, it is actually a piece of free software that has been worked on and improved by volunteers worldwide.
Now, because all the pieces used to build a linux distribution are all seperate programs and not hard coded into the kernel, this means that you can swap them around as you see fit. Getting tired of your usual graphical environment? you can remove it and add a different one, like KDE or fluxbox or GNOME(Most Popular). You can even have 2 or 3 graphical environments installed and choose which one to use when you log in.
This modularity is what makes linux so flexible. You have ultimate control as to what sofware you want on your computer, and that is one of the many reasons why I love it 
In my next post i will explain about the linux distro tree & linux file system, stay tuned.
