The content lifespan is a document that lists every significant piece of content and maps it against a player's journey in the game. It allows people to plan the production, estimate which elements are needed first, and identify the areas that have too many or too few new elements.
Unless you're working on a very open-ended game or a sandbox experience, it should be possible to define a player's vector of progression. This vector will serve as the reference point in the lifespan document. To give a couple of examples: in an open world RPG, the vector of progression might be the player's experience level; in a linear puzzle-platformer, it would be the stages themselves; and in an adventure game, it could all come down to the ...
