"Sau" is also the Romanian word for "or" and the Vietnamese word for "after." Many tutorials in these languages use generic names like sau.rar (meaning "after.rar" or as a placeholder) to demonstrate how to extract or delete archives.
Guides on YouTube or tech blogs like TransferXL explain how to open these files using WinRAR or 7-Zip.
The file might be a compressed archive containing course materials, software-based interactive systems (like the BZK.SAU.FPGA10.1 microcomputer project), or student data.