A payment page is the screen, on a website or in an app, where a customer selects how to pay and enters the details needed to complete a payment. It is the final step of the checkout, after the basket and delivery steps. The page shows the amount due, the accepted methods, input fields for card or account details, and a button that submits the payment.
The main design choice is who serves the page. With hosted checkout the page belongs to the payment provider and the customer is redirected to it; with embedded checkout the provider's secure fields sit inside the merchant's own page. Both keep card data away from the merchant's servers and so limit its duties under the PCI DSS. A page opened from a payment link works without any merchant site. Behind every version, the payment gateway receives the details and requests authorization.