As far as the virtual criminal world is concerned a valid cc refers to the data swiped from the magnetic band at the back of a debit or a credit card (dummy credit card number with cvv), which afterwards might be sold to the interested parties or used for personal enjoyment. It usually provides the card issuerТs identity by means of the INN (issuer identification number) and, secondly, the account number (PAN).
A carding forum is a place where one can illegally interchange or obtain details of a stolen credit card (working credit card details, real visa card number and cvv), usually this type of sites are concealed in the depth of the dark web, where all the shared information is encrypted, for example using TOR routing, and payments for transactions are carried out through cryptocurrencies in order to prevent ordinary people from getting access to it.
The cvv on card or the Card Verification number is a three or four digit number placed on the back side of the credit card. It is commonly demanded when a customer tries to purchase online and its function is to prove to the online merchant that you actually have the physical card, so it is devised to minimize the possibility of fraud (dummy credit card with cvv, random credit card number and cvv). It should not be confused with the card pin code.