In emails, BCC stands for "blind carbon copy". When you put an email address in the BCC field, it means that a copy of the email you are sending will also be sent to that address, but no one receiving the email will be able to see the address in the BCC field. This function can be useful if you want to send copies of an email to other people without revealing their email addresses to the other recipients. It is also a way to protect the privacy of email addresses.