Webhook is a default Switch app that subscribes to specific incoming HTTP requests and injects the received request content as a new job in the flow. The job file name is 'payload' and the file extension is automatically generated from the 'Content-Type' header.
This way, periodic calls using HTTP requests to third-party systems or services (such as an MIS, CRM or W2P) to check for changes are no longer needed. Instead, these systems will now call Switch the moment something has changed (for example, a new order that has been entered), and this will trigger Switch to do something (for example, to create a new job based on this new order).
For more details, see the PDF documentation. Be sure to check the right version, as the setup differs substantially between version 6 and version 7 (and higher).