Bcc

[Sonia]

Stands for Blind Carbon Copy. When you send an e-mail to only one person, you type the recipients address in the To: field. When you send a message to more than one person, you have the option to enter addresses in the Cc: and Bcc: fields. Cc stands for Carbon Copy, while Bcc stands for Blind Carbon Copy.
A carbon copy, or Ccd message is an e-mail that is copied to one or more recipients. Both the main recipient (whose address is in the To: field) and the Ccd recipients can see all the addresses the message was sent to. When a message is blind carbon copied, neither the main recipient nor the Bccd recipients can see the addresses in the Bcc: field.
Blind carbon copying is a useful way to let others see an e-mail you sent without the main recipient knowing. It is faster than sending the original message and then forwarding the sent message to the other recipients. It is also good netiquette to use Bcc when copying a message to many people. This prevents the e-mail addresses from being captured by someone in the list who might use them for spamming purposes. However, if it is important that each recipient knows who your message was sent to, use carbon copy (Cc) instead.

[PussyCat]

Blind carbon copy (used as an indication that a duplicate has been or should be sent to another person without the knowledge of the main recipient).