When the Wii homebrew scene was in its infancy, enthusiasts used the Wii Backup File System (WBFS) to format entire hard drives. Today, the term primarily refers to .wbfs files. This file format is highly optimized for Wii emulation and USB loading for several reasons:
The keyword "upd" in your search likely refers to the concept of your USB loader's cIOS for better game compatibility or updating a large WBFS game collection. 217 wii games wbfs format upd