The abbreviation CC in a memo, or any other physical document, stands for "carbon copy." If it is a digital memo, or other digital document, CC stands for "courtesy copy."
Whether the memo is digital or non-digital, the abbreviation CC essentially means the same thing. It is a copy of a document that is sent to someone other than the original recipient for informational purposes only. The term carbon copy derives from when carbon paper was used to quickly copy documents before computers and printers were widely used. The abbreviation was changed from carbon copy to courtesy copy to make more sense in the digital age.