Downloadable Content, or DLC, was content that the player can choose to buy in addition to the game to add more to it.
Story of Seasons: Trio of Towns had only one DLC - the New Neighbors Pack. This was originally released in Japan for free in four different waves over six months in 2016 and, after much deliberation, was eventually released as paid DLC in North America in February 2017.
NOTE: As of the Nintendo Eshop's closure on March 27th, 2023 this DLC in unobtainable through legitimate means. Players who had previously downloaded it can still access it on their device, but no new players can download it.