I don’t think webhooks need an introduction. But for those who are new to the topic, here you can find the official documentation. In short, a webhook is a push notification. The “don’t call us, we’ll call you” scenario of web services. You tell Business Central in what resource you are interested (e.g. Item, Customer, etc.), and they’ll call you in case there is any change. With resource I mean any of the existing APIs, including custom APIs.