Goodreads Librarians Group discussion

I'm sorry if I am a dolt for not knowing this, but in the list for valid items it says something called "repacks". What is that referring to?
Then over in the non-valid there is "Prepak, ppk, stockpack, stock pack". What are those?

Adding to your question because, in addition to "repacks" and "Prepak, ppk...", there are other mysterious items in these lists. They seem to use jargon that most people don't know. I certainly don't, and I worked at a bookstore for years.

In the valid items article:
- F&C Sheets
- Repacks

In the "invalid items" article:
- 18fl, 24fl, 27fl, 36fl (fl = floor display)
- Awbc
- Clip strip
- Dumpbin, dump bin, dumpb, dumpbi, dumpbn, dbin, d/bin
- >header
- Mixed bin, mixed copy, copy bin, mxd
- Mxfl
- Prepak, ppk, stockpack, stock pack
- Shrinkwrap, shrink wrap, s/wrap, swrap
- x12, x24, x36, x48, 12c, 24c, 36c, 48c, 12cc, 24cc, 36cc, 48cc, 60cc

Also:
- Shorts (my guess is that this means "Short stories", but why use an abbreviation when the two-word term would be clearer?)