What does CC mean in an email?

The term "CC" in regards to email means carbon copy. The carbon copy field is used to send multiple people the same email, similar to typing multiple email addresses in the address field.

Though the carbon copy field has essentially the same function as the address field, it is a useful tool for differentiating between the person for whom the email was primarily written and those for whom it was simply a copy. Similar to the carbon copy field is the blind carbon copy field, which serves the same function as both the address and carbon copy fields except that the the email addresses of all recipients in the blind carbon copy field are hidden from the other recipients of the email.