3-D Secure is a way to authenticate online transactions, similar to enter a PIN code or writing a signature for a transaction on a physical terminal in a shop or restaurant. It was initially developed by VISA under the name "Verified by VISA" and was soon adopted by MasterCard (SecureCode), JCB (J/Secure) and American Express (Safekey®).
There are several forms of 3-D Secure authentication. Depending on the customer's bank and originating country, it can be using a card reader or digipass, entering a PIN-code, or entering a piece of data that only the cardholder can know. 3-D Secure allows merchants selling online to verify that their customers are the genuine cardholder in order to reduce instances of fraud.