The rapid rise of online and mobile retail sales has opened up a new market for payments companies to pursue, and is also creating a new generation of online payment providers called gateways, which act essentially as the online version of an in-store payment terminal.
Companies like Braintree, Adyen, and Worldpay help process online transactions, which are growing much more rapidly than in-store sales.
Payment gateways specifically stand to benefit from the rapid growth of the online processing market, worth an estimated $10.7 billion this year, even though their revenue is a very small slice of the total. BI Intelligence, Business Insider's premium research service, estimates that the US online processing market will increase at a five-year CAGR of 13% to $17.5 billion by 2020, driven by the increase in online shopping volume.
http://www.businessinsider.com/the-payment-gateways-report-examining-the-next-generation-of-payment-providers-competing-in-the-burgeoning-digital-commerce-market-2016-8/