What does it mean for an iPod to be “Over capacity”?

Question

Sometimes when I plug my iPod Nano Shuffle into iTunes, I get this strange message:

What could this possibly mean?

Answer 1

It means that you've set up iTunes to sync certain files onto your iPod, but it can't do so because the total space used by the files that are supposed to be on your iPod is greater than the storage capacity of the iPod. In order to complete the sync you need to take some songs off the iPod.