BCC is an abbreviation used in email, which means simply Blind Carbon Copy. A normal email address can have three classes of email recipients: the To recipients, the CC recipients, and the BCC recipients. The To recipients are thought of as the primary recipients of the email, the CC recipients are those who are receiving carbon copies of the email, and the BCC recipients are those who are receiving carbon copies of the email, but whose addresses no other recipients can see.
The point of the BCC field in an email is to allow for a long list of interested parties to receive the email, but for their email addresses to remain hidden. The recipients listed in the To field are generally thought to be those who the message is actively addressed to, and so a message containing only To recipients has their email addresses exposed to one another, since it is assumed they are working on the same project, or are part of the same group. The CC recipients, on the other hand, are interested parties who are not being directly addressed, and in some situations may be fine knowing each other’s email addresses. The BCC recipients are used when a great number of recipients are included, or people from diverse walks of life, who are unlikely to want their email addresses shared with the larger group.
The BCC field can also be very useful if you want to easily send a copy of an email to someone, without the primary recipient knowing anyone is getting a copy of the email. While this could be accomplished by simply making a second copy of the body of the email and resending it, the BCC field allows for a seamless way to accomplish this in one click. Since the BCC recipient can see the To recipient’s email address and name, if any is included, they know who the email is intended for, but to the To recipient it would appear they were the only person getting the email.
In email mailing lists the BCC field is traditionally used as a courtesy to people who are a part of the list. Even if everyone on the list was okay with everyone else on the list having access to their email address, having such a long list of emails poses a spam risk to everyone on it. Many spam lists are generated by the presence of viruses on a person’s local computer, which harvests email addresses from received emails. A mailing list email can provide a huge list of addresses for such viruses, and the use of BCC means that such a list never exists on anyone except the sender’s computer, greatly reducing the risk of a virus getting the addresses.
The concept of a blind carbon copy actually predates personal computers and email by some time. Typists would occasionally produce many copies of a letter by alternating pages of carbon paper between normal typing paper, so that when the typewriter keys struck the pages they made multiple copies. Addresses and salutations were often left blank during the carbon copy phase, and were then added in by hand later, so that recipients of the letters did not see who else was receiving the letter.