DLC
Also said as Downloadable content, Expansion, Add-on
Extra content sold after the base game. It can be a large expansion or a small item, and players judge the two very differently.
It earns from people who already love your game, without needing to find new ones. It works when it feels like more, and turns sour when it feels like something was cut from the game you already bought.
Say it
“No day-one DLC from content we had finished before launch. Plan one expansion for a year out, with at least ten hours and a new region, and price it at half the base game.”
Where you’ve seen it
The Witcher 3's Blood and Wine is roughly a game in its own right, and players felt they got more than they paid for. Oblivion's $2.50 horse armour in 2006 became the standard joke about the opposite.
Not to be confused with microtransaction
DLC is usually a fixed piece of content you buy once. A microtransaction is a small repeatable purchase, often of currency or a consumable.