Resource Packs

Resource Packs allow for the customization of client resources through the assets directory. This includes textures, models, sounds, localizations, and others. Your mod (as well as Forge itself) can also have resource packs. Any user can therefore modify all the textures, models, and other assets defined within this directory.

Creating a Resource Pack

Resource Packs are stored within your project's resources. The assets directory contains the contents of the pack, while the pack itself is defined by the pack.mcmeta alongside the assets folder. Your mod can have multiple asset domains, since you can add or modify already existing resource packs, like vanilla's, Forge's, or another mod's. You can then follow the steps found at the Minecraft Wiki to create any resource pack.

Additional reading: Resource Locations