Mods
Mods are “modifications” to a game or virtual world.
Modding is the creative act of making mods.
Sometimes mods are made for free as a creative project; at other times, mods are sold as enhancements to a game. In the latter case, modding may be part of a creator economy around the game in question.
Some of the largest games in the world today began as mods: Counterstrike, PUBG and DOTA are three examples.