bin/

Where binaries (immediate executables) are located

boot/

Where the kernel (the heart of the system) lies.

dev/

Where device files lie.

etc/

Where configuration files lie.

home/

Where home directories lie.

lib/

Where libraries and drivers (modules) lie.

lost+found/

Part of the file system (ext2fs)

misc/

Miscellaneous files (usually empty)

mnt/

Where other (non native) partitions are mounted

opt/

Optional files and programs (usually external installed programs)

proc/

Kernel's configuration interface

root/

Root's home directory.

sbin/

Root's Binaries (executables).       

tmp/

Temporary data

usr/

Where programs lie

var/

Where variables lie. Logs, mail and print spool, etc.