Learn in the textbookHow Email Works and Specifying Recipients
Definitioncc (carbon copy) is the address field for people you want to keep informed, and all recipients can see those addresses.
ExplanationTo is for the people the matter directly concerns, while cc is for those you would like to look it over for reference. Addresses in cc go into the message's address information, so recipients can tell who else was copied.
AnalogyLike circulating a report with "FYI: section manager" on the distribution line. Everyone can see who got it.
Memory hookShort for carbon copy, from the old office practice of making a duplicate with carbon paper and handing it to someone else.