istio.io/content/en/docs/reference/glossary/service-mesh.md

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Service Mesh

A service mesh or simply mesh is an infrastructure layer that enables managed, observable and secure communication between workload instances.

Service names combined with a namespace are unique within a mesh. In a multicluster mesh, for example, the bar service in the foo namespace in cluster-1 is considered the same service as the bar service in the foo namespace in cluster-2.

Since identities are shared within the service mesh, workload instances can authenticate communication with any other workload instance within the same service mesh.