Modding
Modding is the process of altering Minecraft’s default experience to add or change features, game mechanics and gameplay.
Mods and other Project types has greatly extended the already infinite possibilities of Minecraft. Today modding has become mush easier than the past but its still a hard thing to do because Minecraft is not designed to allow modifications apart from Resource packs and Datapacks.
Datapacks can extend the Vanilla experience but are not suitable to add new great things and without Loaders modding would not be possible.