The first question most people have when they start working with Linux is "what's a distribution?"
Here is my simple explanation of what a Linux distribution is:
A distribution is a collection of applications and configuration utilities built around the GNU/Linux Operating system.
But, what does this really mean? Why not a single distribution with all the same applications and configurations?
Different people need their computer to perform different tasks: Some write programs some others write documents and prepare presentations some others use them as a web server or to unfold the human genome.
A home computer needs different programs than a web server. Home users are used to GUIs while a web server may not even have one.
What's more even among home users some are experts and some are novice. Some have new and fast computers while some others have older and slower computers.
So, if you want to configure your computer exactly as you want or need, you could search for all the applications you need and install them. In practice only a few curious (and maybe a bit masochist) people dare to start from zero. Some people have already prepared a collection of applications for different "user profiles". They distribute this collections, some free, some commercially. These are the "Distributions".
That does not mean that you can only use the applications provided. Think of a distribution as your starting point. The better you choose your distribution according to your needs, the closer you will be to have a computer configured specifically for you.
As an example of distributions, RedHat (the company) has the following ones:
- Red Hat Enterprise Linux AS : This is a distribution geared to enterprise servers with all the tools to administer a network and its applications
- Red Hat Enterprise Desktop : This one is geared to Desktop users in an office environment.
- Fedora Core : This is a general purpose distribution assembled with 100% free software.
There are 'purpose specific' distributions, for example your TV top-set may be using Linux. Many cell phones use Linux as their underlying OS. There are distributions to configure computer clusters (Groups of computers working as if they were a single one)
Here you can find a list of distributions. Search based on your needs or curiosity and read the descriptions: