Explanation:

In email, BCC stands for Blind Carbon Copy. When an email is sent using BCC, the recipients in the BCC field are invisible to all other recipients of the email (including those in the To and CC fields). This is used for privacy or when sending to a large group without revealing everyone's email address. Options (1), (2), and (3) are incorrect as 'Blue', 'Black', or 'Blank' are not part of the standard acronym for this email function.