I always used to think cc stood for "courtesy copy" – because you're only sending it to someone for information, or maybe out of courtesy because they're named in it.
In 2017 (while investigating the issue for another website) I came to the conclusion that I was wrong, as most dictionaries seemed to give 'carbon copy'. But even then, some dictionaries (e.g. Wiktionary) gave "courtesy copy" as an alternative meaning.
Wiktionary implied that this alternative meaning only applied in the context of emails, where the idea of a carbon copy is clearly pointless; but I pointed out (on that other website) that I'd understood "cc" to mean "courtesy copy" long before I'd even heard of emails.
Three years later, it seems that Wikipedia, at least, has come round more to my way of thinking. It gives both 'carbon copy' and 'courtesy copy' as expansions of 'cc'; on its carbon copy page it doesn't mention emails, but it defines courtesy copy as either "a carbon copy" or "a copy of an email sent to a person other than the main recipient, to keep them informed."
Even in 2017, I concluded that if setting this as a quiz question, you should be prepared to accept "courtesy copy" as an answer. This would seem to be even more true now!
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