The Filesystem Hierarchy Standard (FHS) is a set of directories that should exist in every Linux distribution. The reason for having the Filesystem Hierarchy Standard is so that regardless of the distribution being used, the structure of the filesystem will be the same. The Filesystem Hierarchy Standard has the following directories under the / (root) directory.
The /bin (binary) directory contains binary files, such as /bin/ls and /bin/pwd. The binary files are commands that can be run by anyone - these commands do not require elevated privilege to be execute.
The /boot directory contains files related to booting the computer, such as the GRUB configuration file and the initrd image.
The /dev (devices) directory contains files for both physcial and virtual devices, such as /dev/ha1 (hard disk drive), /dev/sda1 (solid state drive), and /dev/tty1 (first virtual console).
The /home drectory contains each users personal files and folders.
The /lib (library) directory contains shared library files used by programs and kernel modules.
The /media directory is typically used to mount devices such as USB flash drives, CDROM drives, and smart phones.
The /mnt (mount) directory is typically used to mount remote shares, such as Samba or NFS share.
The /opt directory contains files and folders for software, such as a package installed on the PC.
The /proc (processes) directory contains files for each process, such as /proc/meminfo and /proc/cpuinfo.
The /sbin (super user binary) directory contains binary files, such as /sbin/shutdown and /sbin/ifdown. The binary files are commands that require elevated privilege to be executed.
The /sys (system) directory contains files for drivers to talk to applications.
The /temp (temporary) directory contains temporary files.
The /usr directory contains most of the system programs and libraries, such as /usr/bin, /usr/lib, and /usr/local.
The /var (variable) directory contains files that can change, such as log files (/var/log/messages) and website files (/var/www/html).