The term completionist can mean different things to different people. My 100% completion of Bravely Default resulted in getting all characters to level 99, maxing all the jobs and getting true ending. Skyblade on the other had may still be playing bravely default in his quest to see all the dialouge, get 99 of each item, fight every optional boss for the 3rd time or so.

To me it's seeing everything there is to see in a game before throwing in the towel and calling it a day.