A webhook is an automatic notification one system sends another the moment an event happens: payment received, form submitted, order shipped. Where an API is asked (pull), a webhook announces (push). Real-time automation is usually built on webhooks — no polling, no delay, no missed events.
A reliable webhook setup needs retries, signatures and logging — the unglamorous plumbing that separates an automation that works from one that silently drops events, and part of every automation build.