BCC means Blind Carbon Copy
BCC means blind copy and is used when sending an email. With the receivers it is often possible to also fill in a BCC receiver field. When you use the Bcc field, it means that the normal recipients of the e-mail cannot see the BCC email addresses. It seems as if the people in the BCC field do not receive the mail, from a privacy point of view it is good to do so. Also to reduce unwanted mail it is useful to use Bcc: reply to all or reply to all has no effect on the Bcc people. In business, BCC is often used if the recipient is not allowed to know that the message is also sent to others.