Definition
A payment gateway is the technical and contractual layer that sits between a buyer paying with a card or wallet and the merchant receiving the money. It captures the payment details, runs them through the card networks for authorisation, screens for fraud, and settles the funds into the merchant's account on a defined schedule.
In practice the term covers a wide range of products. Stripe, PayPal, Adyen, SumUp, Square, and Wise Business all act as gateways for at least part of the flow, even though they differ in pricing, settlement speed, and supported payment methods. Some gateways are also acquirers (they hold the merchant account); others integrate with separate acquirers behind the scenes.
Why it matters
Your gateway choice quietly determines a meaningful share of your variable cost. The headline rate is only one input — fixed fees, international surcharges, currency conversion margin, and refund and chargeback handling all flow through this single relationship. Picking once and never reviewing leaves money on the table for most growing small businesses.
Where this appears in your tools
The Payment Gateway Optimizer compares total cost across gateways using your real transaction profile rather than headline rates. The Profit Leak Analyzer surfaces effective payment rate as one of the cost lines that quietly compresses margin.
Example
A merchant on Stripe at 2.5 percent + 0.25 processes 50,000 in card volume a month. Headline cost: 1,250 + 200 transactions x 0.25 = 1,300. Real cost after international surcharges and FX margin: roughly 1,580. The gap is paid out of margin, every month, until the merchant either changes provider or restructures their checkout.
Common confusion
A gateway, an acquirer, and a payment processor are not exactly the same thing — but for most small business purposes they are bundled into a single product and a single fee. Worry about the bundled rate; only care about the distinction once you are at a scale where you negotiate components separately.