You download a backup, software package, or dataset and find a file with an unusually long extension: something.tar.zst It looks like two file formats have somehow been glued together. That is essentially what happened — but each part has a different job. The .tar part bundles files and folders together. The .zst part compresses that bundle. Understanding the difference also explains why these files can be awkward to open on a Mac. Two formats, two jobs ZIP is both...