Synchronous integration is a method used in B2B SaaS where data from a third-party app is needed immediately, requiring a webhook URL call and a prompt response to confirm data processing before proceeding with subsequent tasks. This process is exemplified by an integration involving the Acme app, QuickBooks, and Amazon SES, where an order request triggers a series of actions to check inventory, create invoices, and notify users of order statuses. The integration is designed to update the Acme app with a status confirmation, distinguishing it as synchronous, though it could also be adapted to run asynchronously if needed. The choice between synchronous and asynchronous integration depends on specific business requirements, and Prismatic's integration designer offers tools to simplify these processes, allowing for easy transitions between synchronous and asynchronous setups as necessary.