I see that for every knative service, 2 VirtualService objects are created namely ksvc-ingress which has knative-serving/knative-ingress-gateway & knative-serving/knative-local-gateway gateways configured and ksvc-mesh which has mesh as the gateway.
I can see the knative-serving/* gateways using kubectl but I am unable to find the mesh gateway object in any namespace. I would like to understand if mesh here denotes some special object or is it an istio keyword representing something else?
The mesh name is a keyword, as you guessed. That keyword represents the East-West traffic between Pods in the Kubernetes cluster, as managed by the Istio sidecar. You can think of those VirtualServices as being programmed onto each sidecar to do the routing and traffic splitting next to the request sender, rather than needing to route to a central service / gateway.