
It's a ten-year agreement between Bungie and Activision to continuously update the game.
From Wikipedia:
Prior to the official release of Destiny in September 2014, Bungie declared that a major component of the game would be a continuous release of new content. Bungie Director of Production Jonty Barnes said: "We're going to continuously update the game from now until the end of time. That's always going to be part of the philosophy of Destiny. We always wanted to build a new universe but keep building upon it, rather than to do a complete and utter restart periodically."[76] By the time of Destiny's launch, two planned packs of downloadable content (DLC) had been officially announced: The Dark Below and House of Wolves.[77][78] From the launch of Destiny, players could purchase the Destiny Expansion Pass, which included the first two expansions at a discounted price versus buying them separately.[79] Players also received an exclusive sparrow (EV-30 Tumbler) if they purchased the Expansion Pass or The Dark Below by January 15, 2015.[80] At E3 2015, Bungie officially announced a new expansion called The Taken King.[81]