> Operating systems do blur the boundaries of this a bit, now -- you can explore zip files as if they were folders, mount disk images from files, and you can wo

> Operating systems do blur the boundaries of this a bit, now -- you can explore zip files as if they were folders, mount disk images from files, and you can work with folders as bundles (e.g. a macOS application is a disguised bundle, an RTFD document is a directory with contents etc.) Also, AIUI, "Save entire page" in some browsers. You might think that should be a single .html file, but it's usually an .html file plus a directory of stuff linked in that file / on that Web pge, that the browser (and sometimes the OS) then does its best to pretend is just a single file.