A file with .usdz is a ZIP archive for the USD (Universal scene description) file format that contains and proxies for files of other formats embedded within the archive.
GLB is the binary file format representation of 3D models saved in the GL transmission format (glTF). Information about 3D models such as node hierarchy, cameras, materials, animations and meshes in binary format. This binary format stores the glTF asset (JSON, .bin and images) in a binary blob. It also avoids the issue of increase in file size which happens in case of glTF. GLB file format results in compact file sizes, fast loading, complete 3D scene representation, and extensibility for further development. The format uses model/gltf-binary as MIME type.