Linux File System Layout

Below are file system layout that is commonly used by Linux distribution:

• /bin, /usr/bin: directories with user level command binaries
• /sbin, /usr/sbin: directories with administrator level command binaries
• /lib, /usr/lib: directories with static and shared libraries
• /usr/include: directory with include files
• /etc: directory with configuration files
• /var/log: directory with system log files
• /usr/share/doc: directory with various documentation files

(Source: http://techbu.com)

Details of Filesystem Hierarchy Standards are available here