Originally Posted by Ciclop
What exactly does this mean?
What exactly is ROM and Kernel?
The easiest way to think of a ROM is that it is your phones operating system. A rooted android device can change this. Developers have customized ones that add different functionalities or settings not available on the stock ROM. They are able to do this because of the open source nature of android.
You can also install different versions of android ahead of when the device gets officially updated. I am running the newest version of android (Jellybean) on my phone using one of these custom ROMS (cyanogenmod 10) even though my device hasnt been officially upgraded by the manufacturer yet.
Kernels are sort of the gap between the hardware and the software. Like ROMS, these are open source as well so developers can make changes to them to make them perform better or save more battery. There are even functional things that can be added here as well such as USB host mode or 2 way call recording.
All of the above requires a rooted phone. If you are interested on reading up on more of this, here are some links for you to check out
What is root or being rooted mean?