Webhook
A webhook is a message one system sends to another automatically when a specific event happens, so the receiving system learns about the change immediately instead of asking repeatedly.
Why the direction matters
Polling an API on a schedule means the process is only ever as current as the last check. A webhook reverses that: the source system pushes the event as it occurs. Where response speed is part of the outcome — a new enquiry, a failed payment, a booking change — that difference is the whole point.
What has to be handled for it to be reliable
Webhooks can arrive twice, arrive out of order, or fail to arrive because the receiver was briefly unavailable. A production integration therefore needs deduplication, a retry path, and a record of what was received. This is ordinary engineering work, but it is work, and it is a fair thing to ask a vendor how they handle.
Security
A webhook endpoint is a public address that accepts messages, so the receiver must verify that a message genuinely came from the system it claims to come from, usually through a signature. An unverified endpoint accepts anything anyone sends it.