The Minecraft Resource Pack system is an API replacement for texture packs and a way for players to further customize their Minecraft experience.
Resource packs allow players to customize textures, music, sounds, language files, end credits, splashes, and fonts without any code modification.
If the resource pack system supports modification and addition of code in future updates as mentioned by Mojang, every mod/plugin will be its own resource pack, with vanilla incorporated as a resource pack by itself; users will be able to apply multiple resource packs at once. However, for security reasons, there would be limits to what could be modified. Executing unstable code could corrupt a client copy of Minecraft.
This function would be great for adventure maps where you'd want to change the music of a certain disc, or if you'd want to change the end credits to something more user-friendly. Or it could be useful to a server that wants specific textures on the server. You could even change the name of the item itself in Survival maps. And of course, changing the textures of things like texture packs have done. Keep in mind that you can also change the words of the Death Messages, Title-Screen options and some other things.
