A webhook is a way for one application to send real-time data to another the moment an event happens, by making an HTTP request to a URL that the receiving application provides.
The receiving application registers a URL, called an endpoint, with the sending application. When the chosen event occurs, the sender makes an HTTP request to that endpoint, delivering a payload, usually formatted as JSON, that describes what happened.
With polling, your application repeatedly asks another service whether anything has changed, and most of the time there is no news. A webhook reverses this: the service sends data to you only when there is something new, so it is more timely and avoids wasted repeated requests.
Because the endpoint is a public URL, the receiver should verify that each request genuinely came from the expected sender, commonly by checking a signature that the sender includes with the payload. The receiver should also acknowledge receipt promptly; if it does not, senders typically retry delivery.
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