Obviously your phone is rooted, but are you running the custom clockwork recovery? Nandroid backups are a function of recovery menus, and are essentially just complete backups of your phone's internal memory.
So for instance, you make a nandroid backup before you do something potentially risky to the phone. If you mess something up, then you restore the nandroid backup and the phone is exactly as it was before you messed around. They are extremely handy things to have.
In the case of the flashing to stock thread, somebody has made a backup of a phone running the stock firmware, which you can restore on your phone to get it working again.
If you aren't using a recovery image at the moment however, then you'll need to pick the other method.
So for instance, you make a nandroid backup before you do something potentially risky to the phone. If you mess something up, then you restore the nandroid backup and the phone is exactly as it was before you messed around. They are extremely handy things to have.
In the case of the flashing to stock thread, somebody has made a backup of a phone running the stock firmware, which you can restore on your phone to get it working again.
If you aren't using a recovery image at the moment however, then you'll need to pick the other method.


