Webhook
HTTP call one system sends to another when an event occurs. An efficient alternative to polling.
A webhook is a mechanism where one system notifies another when an event occurs ("an invoice was paid", "a user signed up") by sending an HTTP call with the data. It's the opposite of polling, where one system constantly asks "anything new?". Webhooks are the basis of efficient modern integrations: Stripe, GitHub, Slack, HubSpot, and most SaaS support them. Well-implemented they save resources and react in real time.