Source : Free On-Line Dictionary of Computing

case sensitivity
     
         Whether a text matching operation distinguishes
        upper-{case} (capital) letters from lower case (is "case
        sensitive") or not ("case insensitive").
     
        Case in file names should be preserved (for readability) but
        ignored when matching (so the user doesn't have to get it
        right).  {MS-DOS} does not preserve case in file names, {Unix}
        preserves case and matches are case sensitive.
     
        Any decent {text editor} will allow the user to specify
        whether or not text searches should be {case sensitive}.
     
        Case sensitivity is also relevant in programming (most
        programming languages distiguish between case in the names of
        {identifiers}), and addressing ({Internet} {domain names} are
        case insensitive but {RFC 822} local {mailbox} names are case
        sensitive).
     
        Case insensitive operations are sometimes said to "fold case",
        from the idea of folding the character code table so that
        upper and lower case letters coincide.  The alternative "smash
        case" is more likely to be used by someone who considers this
        behaviour a {misfeature} or in cases where one case is
        actually permanently converted to the other.
     
        "{MS-DOS} will automatically smash case in the names of all
        the files you create".
     
        (1997-07-09)