2018 Topps 80th Anniversary Wrapper Art Non-Sport Forum

what does PR mean? Press Run of how many actual cards were printed?

Yes, it's the "Print Run" - the definition is listed in the Glossary for the set.

Different from SN (Serial Numbered) cards. Press Run may or may not have the quantity of the run on the card;

Whereas a SN card has the edition number listed of the total press run;

It's also used when the total print run of the card is known (usually published by the manufacturer or a hobby publication) but not necessarily printed anywhere on the card.

And there's another interested case where it's used in conjunction with "SN". Sometimes a number of cards are printed and the first x number of cards have a special feature, such as die-cutting or different colored ink for an autograph. So in the case of a serial-numbered insert limited to 1000 copies, with the first 100 cards being die-cut, cards 1-100 would have the notes "PR100, SN1000" and then 101-1000 would be "PR900, SN1000".