Card acceptance infrastructure is the combination of equipment, software, connections and contracts that allows merchants to take card payments. In shops it starts with the payment terminal or point-of-sale system, which reads chip, contactless or wallet credentials. Online, it starts with a checkout page and a payment gateway. Behind these sit the acquirer and processor, the card networks that carry messages between acquirers and issuers, and the security standards that protect card data, such as EMV and PCI DSS. Policymakers measure acceptance infrastructure by counting terminals or accepting merchants per head of population, and low density is a common barrier to card use in developing markets. Lower-cost options include mobile point-of-sale readers and acceptance on ordinary phones. Also see digital payment acceptance.