The following definitions are from: The Linux System Administrator's Guide
(Chapter 3.2) located at The Linux Documentation Project
/bin Commands needed during bootup that might be used by normal users (probably after bootup).
/sbin Like /bin, but the commands are not intended for normal users, although they may use them if necessary and allowed. /sbin is not usually in the default path of normal users, but will be in root's default path
Hope this helps!