BCC
BCC stands for blind carbon copy.
Using BCC in an email means only the sender can see the full list of recipients, adding a layer of security in terms of data protection.
Another way to understand BCC is that it's the opposite of CC, which allows everyone who has been sent the email to see the other recipients of the message.
While CC is fine for internal communication, it wouldn't be suitable for external communication (whereby email addresses need to be protected), hence why BCC is used instead.
Example
When sending an email to a group of people who aren't known to each other, i.e. they are customers rather than being part of your internal team. Usually, BCC is for sending mass emails which don't require a response.
BCC is also ideal when emailing customers about a change of details, whereby you need to send the same message to everyone but don't want the recipients to see other recipients.
Or, if having a conversation with a customer and you want to tag in a manager, using BCC will allow your manager to view the messages without the customer being able to see.