If you would send emails to people, you may notice that there are two slots that are available wherein you can place email addresses. You can place the email address on the CC or the BCC. When you say CC, this means carbon copy.
You will be putting the email addresses of people who would also like to know the other people to whom the email has been addressed. When you say BCC, this means blind carbon copy.
The email addresses of the people that you would place there will not be visible to other people. This can be helpful when you want the recipient of the email to focus on the actual subject matter of the email as compared to the number of people who have received the email.