" ERE" – Eastern Roman Empire, as alternative name for the Byzantine Empire.
" OPM" – One-province minor this acronym signifies a usually independent nation consisting of only one province.
" WAD" – Works/working as designed this acronym means that the thing in question is functioning as intended, typically used in the context of a mistaken bug.
" GG" – Gamersgate, one of the retailers of CKII.
" PI" – Paradox Interactive, the publisher of CKII.
" PDS" – Paradox Development Studio, the developers of CKII.
" CK2" or "CKII" – Crusader Kings II, the game you are on the wiki for.
These are the acronyms (initialisms) related to CK2 that you'll find on the Paradoxplaza forums: