Linux provides access to some operating system (kernel) data structures directly through "file-like" access.

The proc file system uses file operations to provide names and access to certain kernel data.

There is a "directory" named proc and its path is /proc.

The directory contains other directories and pseudo files.

A pseudo file has a name. You can list the pseudo file and list its contents, provided the permissions allow it.

However, listing such a file often shows that it contains 0 bytes, eventhough listing its contents shows some data.