A lot of them are the first three letters of leader traits (IND = Industrial, PHI = Philosophical). Besides that, NTT = no tech trading (something which does make deity significantly more difficult), EE = espionage economy (i.e. using espionage point generation to steal techs instead of researching them), OP = overpowered. Also in that post he uses TGL for the Great Lighthouse (I think?) but other people use TGL for The Great Library and GLH for Great Lighthouse.