Can someone explain to me the meaning of novelty only prior art, and the difference between this and regular prior art? Thanks.
You have a relevant discussion about this topic here. It refers to the European patent practice but could be valid for many other jurisdictions.
Pretty much, the novelty requirement is meant to avoid 2+ patents on the same subject-matter in a same jurisdiction, otherwise a third party will have to get 2+ licenses for the very same subject-matter, which is unfair given that they are for the same invention. By limiting the novelty requirement to patents and patent applications of a same jurisdiction you could have the same monopoly in the respective jurisdiction and somewhere else, and that somewhere else is not a problem because the third party needs the license per jurisdiction.