A webhook is an HTTP callback. You register a URL with a service, and the service sends an HTTP request to that URL whenever a specific event happens: a post is published, a payment clears, a build finishes.
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Webhooks versus polling
Without webhooks, your system has to poll: ask the API over and over whether anything changed. Webhooks invert the flow. The provider tells you the moment something happens, which is faster for you and cheaper for both sides. With a social media API, the same choice decides how your app learns that a scheduled post went live: it polls the job status or receives an event.
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Handling webhooks reliably
Webhook handlers should respond quickly, verify the sender (usually via a signature header), and be idempotent: the same event may be delivered more than once, so processing it twice must not corrupt your data.
Go from the definition to the docs that show how to apply it.
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