Webhook
A reverse API call — a platform sends your app a message the instant an event happens, instead of you having to poll for it.
A webhook is an automated callback: you register a URL, and the platform POSTs to it whenever a specific event occurs — a new comment, a mention, a failed post. It's the push to an API's pull, so your app reacts in real time without repeatedly asking "anything new yet?"
For social tools this powers instant notifications — a fresh comment can ping your app the moment it lands, letting you reply while the thread is still warm rather than discovering it on the next scheduled check.
See also