Yaz0
Yaz0 is a compression algorithm used in many Nintendo games.
Structure
The structure is documented on the MK8 wiki.
Usage in Breath of the Wild
Yaz0 is the only compression algorithm that is used in Breath of the Wild. Many resources, such as bactorpacks and BYMLs, are compressed. However, content files that are inside of archives that have already been compressed (such as ActorParam files) are typically uncompressed.
Extensions that start with an s indicate that the file is compressed using the Yaz0 format. For consistency reasons and to reduce visual noise, ZeldaMods (Breath of the Wild) chooses to omit the prefix when referring to file extensions.