American Express is a credit or charge card that can be used for online payments. American Express is amongst the major credit card brands in the world.
Discover is one of the major global credit card brands in the World. Discover (+Diners) has around 110 million cardholders worldwide, 55 million in the US. Discover cards can also be used for online purchases and act similar as MasterCard and Visa.
A direct debit is a transaction whereby funds are withdrawn from the customer's bank account. When a shopper selects the direct debit payment option upon checkout, the merchant is allowed to charge the purchase amount and collect it from the shopper's bank account.