system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the function of the 3 digit "security code" on your credit card when you have to provide it every time you use your credit card?

IIRC, it used to be a way to prevent fraud by people who had your cc number and expiration (say from a restaurant receipt) but not your physical card, but today there are very few people on earth who have my cc number and expiration but don't have my 3 digit code.

At this point it seems like nothing more than a 3 digit extension of your credit card number.
gpt
Its for what are called "Card not present" transactions. Its an additional layer of security to prove you have the physical card.

When you go to a store and pay with your card, you have teh card, nothing else is really needed. Thats why you don't use your CVV. They physically can run the card.

But, what about when you buy a shirt online? This is a "card not present" transaction.  How does the merchant know you have the card and its not fraud or scam just with the number? Well, thats where the 3 digit CVV comes in, it proves you have the card and fraud is much less likely. 

None of this prevents fraud entirely, but it significantly helps reduce it.