/boot -> Grub.cfg
/root -> home of root
/dev -> system device (mouse, keyboard)
/etc -> configuration files
/bin -> /usr/bin -> everyday user commands
/sbin -> /usr/sbin -> system/filesystem commands
/opt -> third party app (not part of os)
/proc -> running process (only in memory)
/lib -> /usr/lib -> C prog lib
/tmp -> temporary folder
/home -> user dir
/var -> system logs
/run -> system daemon -> store temporary runtime / PID file
/mnt -> mount external file system
/media -> CDrom