Partitioning my sd card????

I see this term alot and usually just brushed it off until I saw something about saving a boatload of internal memory soooooo can someone point me to a post or something or just give me a quick rundown (in laymens terms) of what it means .


If i flash a rom and do this does that mean the rom is running off the sd?? how am i saving memory.

 

ok, im gonna back up everything and give this a whirl, I figured out rooting and flashing roms without damaging anything so this shouldnt be different

 

so how do i confirm it worked, i just used joeneidy's custom recovery to do it