Carbon Copy

This is a method of sending a copy of an e-mail to someone, but implying that they are not the direct recipient. For example, you send an e-mail with instructions to a group you manage, and CC it to your boss so that they know what's going on, but understand that the instructions in the mail were not meant for them to carry out. When you carbon copy someone in an e-mail, the recipients in the To field of the e-mail are aware of the names in the CC field. If you want to keep names a copy of a message which all persons on the Cc: list receive. Recipients of the message can see who else it has been circulated to.

carbon: a copy made with carbon paper

Carbon copying, often abbreviated to c.c., is the technique of using carbon paper to produce several copies of paper documents. On an old-fashioned typewriter, this would be done by placing the carbon paper between two sheets of paper in the machine, so that whatever was typed on the front sheet was copied onto the second sheet. This technique applies to written documents as well.