Resource pack

The resource pack system is an API replacement for texture packs and a way for players to further customize their Minecraft experience.

Resource packs eventually allow players to customize music, sounds, language files, end credits, and fonts without any code modification. Ultimately, 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.

Texture Packs
All texture pack functionality has been incorporated into resource packs as of 1.6. All prior texture packs must first be converted to be usable by the game. A tool called Minecraft Texture Ender is available from Mojang to manually convert "unstitched" (1.5 compatible) texture packs to resource packs. "Stitched" packs, which are texture packs meant for versions prior to 1.5, must first be unstitched with Unstitcher. Converted packs function as texture packs when loaded in the game.

Additional functionality
Resource packs include a new metadata format that allows plugin developers in addition to Mojang themselves to easily include whole new types of resources such as sounds, language files, music, etc. with minimal difficulty. The new format will also allow Minecraft to more easily detect out of date packs, while still being able to load them. Resource packs use the entire assets folder in the minecraft directory and "1.6.jar" (a new version format in the new launcher) for usage of additional resources, and include pack.mcmeta (used to describe the resource pack like pack.txt before 1.6), and pack.png (a picture for the resource pack, same as texture packs).