Finding the CIN of MTG Cards for collection on recent (2017-ish) MTG cards
"CIN" probably stands for "Card Identification Number" or something similar, just based on context. This does not appear to be a commonly used term online when discussing Magic: the Gathering.

The abbreviation for each set is officially decided by Wizards. You can find these abbreviations at http://en.wikipedia.org/wiki/List_of_Magic:_The_Gathering_sets or http://mtg.wikia.com/wiki/Set.