Postback, in general, are URLs that are used to transfer the information about conversion. They are sometimes called callbacks, server-to-server (S2S) or cookie-less conversion tracking. Postback allows servers to communicate with each other directly. If a client is not involved, no cookies would be used on a visitor’s computer. Once get activated by a source platform (an affiliate network or tracker), these links would send information to the target platform (a tracker or traffic source) in a blink of an eye.
In short, Postback URL refers to the process of getting notified about a conversion event via a third-party server.
Enabling Postback URL allows your affiliates to enter their postback URL with parameters so the required information will be sent to their third-party server.