Here is a good introduction about what is linux and there is a little more information that can be useful for you:

http://tldp.org/LDP/intro-linux/html/chap_01.html


Enjoy!.

I will avoid giving links in case they disappear in the future.

Linux is only a kernel, which is a set of drivers that allow software and hardware to interact with hardware. The Linux based distributions are full operating systems that operate on top of the Linux kernel and have various applications and libraries installed to give you a fill complete experience.