Definition
A webhook is a lightweight, event-driven HTTP request that one system sends to another when something specific happens. Unlike a traditional API call where your software has to ask "anything new?" on a schedule (polling), webhooks flip the model: the source system pushes a payload the instant an event fires, so the receiver gets the data immediately with zero wasted requests.
A webhook is just a URL. The sender posts a JSON body to it; the receiver parses the body and does something useful. That is the entire protocol. Webhooks do not replace APIs, they complement them. APIs are how you query or modify state. Webhooks are how you learn that state changed.
How SheetLinkWP relates to Webhook
SheetLink Forms uses a webhook-style delivery model to send every WordPress form submission to your Google Sheet. When a visitor submits a form, the plugin fires an HTTP POST to an Apps Script web app you deploy inside your own Google account. The Apps Script reads the payload, appends a row to your sheet, and returns a status code. No third-party cloud relay, no per-request fee, no polling.
Your Apps Script endpoint is private to you. The webhook URL acts as an authenticated destination, and SheetLink additionally signs each payload with a shared secret so your sheet can reject forged requests. The Retry Queue built into the plugin will retry failed deliveries with exponential backoff, so a momentary Google outage does not lose submissions.