Webhooks are user-defined HTTP callbacks that enable real-time communication between web applications by notifying a system of changes immediately, rather than requiring continuous polling like standard APIs. They operate on a publish/subscribe model, where an event, such as a change in data, triggers the webhook to deliver a payload—a set of data or entire record—to a specified endpoint URL. Unlike APIs that are reactive and respond to specific requests, webhooks are proactive, sending data as soon as it changes, making them more efficient for time-sensitive data transfers. For example, in a B2B SaaS context, a webhook could notify a Slack channel whenever a new account is created in a SaaS app, requiring data transformation for compatibility with Slack's message structure. Webhooks can be simpler to implement than standard APIs and are particularly beneficial when immediate data updates are essential, though they are not suited for every scenario and are best used in conjunction with APIs. The Prismatic platform exemplifies how webhooks can be effectively integrated into SaaS products to enhance real-time data communication.