Sometimes after you finish a game main storyline the game doesn't end there, and presents other opportunities to finish old quests or perhaps unlock new areas.
Examples of this are like Fallout 3 (with DLC), which allowed you to continue playing and completing quests even after the game's main storyline had completed. In fact, it opened up new quests that were previously unavailable had the main storyline not be completed. Another example is Final Fantasy 4 for the GBA; after completion of the game and the defeat of the final boss, you were allowed to access secret areas that opened on the maps as well as take on challenge bosses for fun.
I am looking for the terminology to describe this.