BCC

BCC or blind carbon-copy is a field in most email programs which allows you to identify additional recipients to receive an email message without allowing them (or other recipients in the To and CC fields) to see other recipients' names or email addresses.

BCC can be useful for including third-parties in conversations when you would like to keep their presence in the conversation a secret. For this reason, however, using BCC can be seen as being rude or non-transparent in many settings, and so, it should be used with care.

One use of BCC that is extremely useful is for newsletters and other correspondences where your recipients should not be given one another's names and email addresses.