From Wikipedia:

Visa Inc. (/ˈviːzə, ˈviːsə/) is an American multinational payment card services corporation headquartered in San Francisco, California. It facilitates electronic funds transfers throughout the world, most commonly through Visa-branded credit cards, debit cards and prepaid cards.

Visa does not issue cards, extend credit, or set rates and fees for consumers; rather, Visa provides financial institutions with Visa-branded payment products that they then use to offer credit, debit, prepaid and cash access programs to their customers. In 2015, the Nilson Report, a publication that tracks the credit card industry, found that Visa's global network (known as VisaNet) processed 100 billion transactions during 2014 with a total volume of US$6.8 trillion.