A networking service that unifies connectivity from remote sites (VPN, ExpressRoute, SD-WAN) and VNets into a Microsoft-managed hub, simplifying hub-and-spoke topologies at large scale without needing to manually configure peering between multiple hubs.
On AZ-305 you choose Virtual WAN when an organization has dozens or hundreds of sites/VNets and a manual hub-and-spoke topology becomes unmanageable. It automates routing between hubs (full transitivity), something classic hub-and-spoke with VNet peering doesn't offer natively.
Azure Virtual WAN is a concept that can show up on the exam. Check the full guide to see it in context.