A payment gateway is the technology layer that captures card details at checkout, encrypts them and passes them to an acquirer or processor for authorization. It is the front door of the payment stack: the checkout form or API, the vault that tokenizes card data and the routing logic that decides where each transaction is sent.
Why it matters
A gateway moves data, not money, which is why the label gets confused with payment service providers that do both. The distinction matters most in high risk processing, where merchants often hold accounts with several acquirers: a good gateway routes traffic across MIDs, retries intelligently, orchestrates 3D Secure and keeps card data portable through tokenization. Merchants who let one provider own the checkout, the vault and the acquiring in a single bundle should at least know what leaving would cost.