firmware efi update for macbook pro

I was opening itunes when and it said there was a new itunes version to do an update, I just clicked ok and in the process the computer was also installing a firmware efi update, which I don't know what is... I've been reading around but I haven't quite understood what it is, why my mac jsut suddenly did this update, what does this mean and what this is for, waht is going to be the difference now that the update has been done, what in my mac can be affected by this update...
I'm a little worried as I had never heard about this firmware efi thing until now.

So if someone can help me see the light...

thanks a lot

Apple Firmware Updates info.

Regards.