Friendly fraud is the chargeback opened by the cardholder themselves over a purchase they actually made, without a third party having misused the card. The reasons vary: forgetting the purchase, buyer's remorse not resolved directly with the seller, or a deliberate dispute to get the money back while keeping the product.
Unlike fraud with a stolen card, friendly fraud is not caught by fraud prevention at the moment of purchase, because the transaction itself is legitimate. Defense in this case depends on evidence: proof of delivery, a history of access to the product, communication with the buyer.