Hier mal eine sehr einfach und auch sehr richtige Erklärung:
1) Linux is a Kernel.
2) Linux Kernel is the main component of all Linux Operating System.
3) The word “Linux” can be used to describe both the “Linux kernel” and the “operating system”.
4) Linux has many “distributions”.
5) Linux Distribution is a collection of applications bundled with the Kernel.
6) Ubuntu is one of the many, and the most widely used, Linux Distributions.
7) Linux is a safe operating system and viruses are very rare.
8) Linux is free.
9) Linux is highly customizable, like any open source software.
10) Linux is the leading embedded OS, which means you probably used Linux already without knowing about it.