Does this refer to Digital Rights Management? Is this a way that we can sell our ebooks with a password (or something)?
I don’t know the ‘actual’ answer, but in an internet buffoon way I will venture my opinion anyway. Rights would usually describe what rights you are offering the recipient / reader - eg ‘worldwide print in original language’ / ‘Online exclusive 12 months’ / ‘personal use, multi-copy’ etc.
DRM would be specified as such, as it’s controlled by the seller of the product, and may or may not be technically enabled at point of formatting.
No, this is just a regular meta-data field where you can put © such-and-such-or-whatever - it’s part of the OPF specifications, OPF being one of the fundamental XML files required for building epub and Kindle files.
All the best,
Keith
Rights. As in all rights reserved. 
Thanks for the explanation. Appreciate it.