The document discusses payment gateways. It defines a payment gateway as an e-commerce service that authorizes payments for online retailers. It then describes how payment gateways work in 3 steps: (1) sensitive payment information is encrypted when submitted from the customer to the merchant's server and payment gateway; (2) the payment gateway passes the transaction details to the acquiring bank and issuing bank; (3) the banks process the transaction and send an encrypted response back to the customer via the payment gateway and merchant.