What it means
A webhook is an HTTP request sent by one system to another when a specific event happens. Where an API call asks 'what is the state of X?', a webhook says 'X just changed; here is what happened'. The receiving system can then react: write to a database, trigger an automation, alert a human.
Most modern platforms support webhooks for major events: new message received, lead created, payment completed, status changed. A webhook URL is just a normal HTTPS endpoint that accepts POST requests.
Why it matters
Webhooks are the connective tissue of modern marketing stacks. Connecting respond.io to a CRM, a CRM to an email platform, a payment processor to your AI agent: all of it is webhooks under the hood.
The alternative (polling: asking each system on a schedule whether anything changed) is wasteful and slow. Webhooks are real-time, low-overhead, and well supported.
Example
A property agency's stack: respond.io fires a webhook when a new WhatsApp lead replies. The webhook hits a Make.com scenario which writes the lead into Salesforce, triggers an AI-agent qualification flow, and notifies the assigned agent on Slack. Total latency: under three seconds, end to end.