/proc Filesystem
In the Unix-world, there is commonly a special filesystem mounted at /proc. This filesystem is implemented within the kernel and publishes information about processes. For each process, there is a directory (named by the process ID), containing detailed information about the process: status, open files, memory maps, mounts, etc.
/proc first appeared in Unix 8th Edition, and its functionality was greatly expanded in Plan 9 from Bell Labs.
Read more about this topic: Synthetic File System, Examples