Ok, I need a Nandroid backup for idiots guide.

[Genjinaro]

Just when I thought I could get by with Sprite Backup.

I'm trying to go about updating my ROM safely but I'm desperately trying to wrap my head around the step before as most say "MAKE SURE YOU DO A NANDROID BACKUP etc etc" but What exactly is a NANDROID backup?

....NANDROID,
Is it an backup app or something pre-existing for backups in a rooted Hero?
If so where to get the app? is it an .apk & if not, whats the install method?
After Googling I keep coming across this app Busybox when looking up how to do a NANDROID backup but I also see G1 in the same sentence so I'm not sure if this Busybox is what I need.



Can anyone explain this in full? Or video guide?

(BTW yes my Hero is rooted w/ stock ROM)