The idea is that in a complex game, after most players have finished a first full play-through, the mechanics might still leave interesting things for them to do. An Act 2 game-within-a-game emerges for experienced players who have exhausted the nominal game. A game dominated by such second-order players is an elder game. In Borderlands, the elder game was apparently gun collecting. […] An elder game can be contrasted with a late style, which is a style of creative production taken to an extreme, past the point of baroque exhaustion, in a sort of virtuoso display of raging against the dying of the night. Late-style game play is an overclocked finite game resisting the forces of mortality. An elder game is a derivative infinite game, emergent immortality hacked out of mortality.
via Doug Belshaw