Yaz0 is a compression algorithm used in many Nintendo games.
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.