An exact duplicate.
The term 'carbon copy' derives from carbon paper, which was, and occasionally still is, used to make copies of typewritten documents.
The phrase predates modern photocopiers, but even they use carbon.
The paper, which was originally developed so that blind people could write without the need for pen and ink, is a thin paper coated with a mixture of wax and pigment. It was first referred to in 1806, as 'carbonated paper', by its inventor Ralph Wedgwood, in the patent for his 'Stylographic Writer'. Other forms of inked paper were also developed around the same time, some of them similar to what we would now recognize as typewriter ribbon.
A 'carbon copy' is often referred to just as c.c. This abbreviation has become better known through its use in email. Most email software has the option to 'CC' a mail to a secondary address; 'blind carbon-copies' or 'BCCs' allow the sender to direct a copy to a secondary address but to hide that from the primary recipient.
The first example of the use of 'carbon copy' that I can find relates to Wedgwood's invention, in the Burlington Hawk-Eye, May 1878, written by "J. L. W." and reprinted from the Chicago Post:
"My own plan was to use the Wedgewood carbon copy-book, jetting down scrap notes whenever opportunity offered."
However, that's really an example of a 'carbon copy-book' rather than 'carbon copy' itself; for that we have to wait until March 1888 and a piece in The Newark Daily Advocate:
"Granville brought out a carbon copy of Mr. Booth's Times article."
See also: carbon footprint.