3DS or 3D Secure 

3D Secure is a protocol (set of rules) that provides extra protection for merchants and customers for online payments. It is used to authenticate the cardholder during payment processing, similar to entering a PIN for an ATM or EFTPOS transaction. The basic concept of the protocol is to tie the financial authorisation process with an online authentication. This authentication is based on a three-domain model (hence the 3-D in the name).