Source : Free On-Line Dictionary of Computing

Blind Carbon Copy
     
         (BCC) An {electronic mail} {header} which lists
        addresses to which a message should be sent, but which will
        not be seen by the recipients.
     
        Bcc is defined in {RFC 822} and supported by most e-mail
        systems.  A normal, non-blind "CC" header would be visible to
        all recipients, thus allowing them to reply to each other as
        well as to the sender.  According to RFC 822, the addresses
        listed in a BCC header are not included in the copies of the
        message sent to the recipients.  RFC 822 says BCC addresses
        may appear in the copy sent to "BCC" recipients themselves
        (though this would be unusual).
     
        (1998-03-14)