The Linux kernel makes a special filesystem available, which is
mounted under /proc on Debian systems. This is a “pseudo-filesystem”
because it doesn’t really exist on any of your physical devices.
The proc filesystem contains information about the system and
running processes. Some of the “files” in /proc are reasonably
understandable to humans (try typing cat /proc/meminfo or cat
/proc/cpuinfo); others are arcane collections of numbers. Often,
system utilities use these to gather information and present it to
you in a more understandable way.
People frequently panic when they notice one file in particular—
/proc/kcore —which is generally huge. This is (more or less) a copy
/of
the contents of your computer’s memory. It’s used to debug the
kernel. It doesn’t actually exist anywhere, so don’t worry about its
size.
If you want to know about all the things in /proc, type man 5 proc.