In the Filesystem Hierarchy Standard, what exactly is a "shareable file"?

The [3.0 Filesystem Hierarchy Standard](https://refspecs.linuxfoundation.org/FHS_3.0/fhs-3.0.pdf) mentions Linux hosts and the concept of a shareable file: > "Shareable" files are those that can be stored on one host and used on others. "Unshareable" files are those that are not shareable. For example, the files in user home directories are shareable whereas device lock files are not. [...] Shareable files can be stored on one host and used on several others. Typically, however, not all files in the filesystem hierarchy are shareable and so each system has local storage containing at least its unshareable files. It is convenient if all the files a system requires that are stored on a foreign host can be made available by mounting one or a few directories from the foreign host. However, I can't understand exactly what it means. A "shareable file" is a file that can be shared across a local network of Linux machines (Linux hosts)? How the restriction of shareable/unshareable works in practice (for example, the OS will prevent an "unshareable" file from being "shared")?