Linux Filesystem Hierarchy Standard(FHS)

Linux FHS or Filesystem Hierarchy Standard is the standard linux file system outlet across all distributions.

/boot:  boot related file such as
vmlinuz-2.6.32-279.el6.i686
initramfs-2.6.32-279.el6.i686.img
grub (directory, bootloader)

boot must be in a separated file system

/dev: the preudo file system to contain the device files
    block device: random access, data is organised as block
    char device: sequence access, data is organised as char.
each device is identified by a major and a minor.

/etc：contains the configuration files

/home：user home directory, usually it is /home/USERNAME

/root：super user's home directory

/lib：library files
static linked files .a
 dynamic linked files .so (shared object)
/lib/modules：kernel related modules

/media：mount point used for external device

/mnt：mount point used for temporary usage.

/opt：optional directory. often used by 3rd party program
/proc：preudo file system, used as kernel parameters mapping files.
/sys：preudo file system, used as hardware mapping files.
/temporary directory, another option is /var/tmp
/var：variable files
/bin: user level executable binaries
/sbin：super user's executable binaries

/usr：shared, read-only
/usr/bin
/usr/sbin
/usr/lib

/usr/local：third party program
/usr/local/bin
/usr/local/sbin
/usr/local/lib