Glossary improvements (#4877)

* Glossary improvements

* tweaks

* control plane tweak

* clarify control plane source

* trailing spaces

* Update content/en/docs/reference/glossary/service-mesh.md

Co-Authored-By: Rigs Caballero <grca@google.com>

* Update content/en/docs/reference/glossary/service-mesh.md

Co-Authored-By: Rigs Caballero <grca@google.com>

* Update content/en/docs/reference/glossary/managed-control-plane.md

Co-Authored-By: Rigs Caballero <grca@google.com>

content/en/docs/reference/glossary/control-plane.md

@@ -2,6 +2,6 @@
 title: Control Plane
 ---
 
-A control plane is a set of one or more instances that share the
-same configuration source. The control plane configures the mesh or a subset of
+A control plane is a set of system services that configure the mesh or a subset of
 the mesh to manage the communication between the workload instances within.
+All instances of a control plane in a single mesh share the same configuration source.

content/en/docs/reference/glossary/managed-control-plane.md

@@ -0,0 +1,8 @@
+---
+title: Managed Control Plane
+---
+
+A managed control plane is a [control plane](/docs/reference/glossary/#control-plane)
+that cloud providers manage for their customers.
+Managed control planes reduce the complexity of user deployments
+and typically guarantee some level of performance and availability.

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

@@ -5,7 +5,8 @@ A *service mesh* or simply *mesh* is an infrastructure layer that enables
 managed, observable and secure communication between
 [workload instances](/docs/reference/glossary/#workload-instance).
 
-Service names combined with a namespace are unique within a mesh. For example,
+Service names combined with a namespace are unique within a mesh.
+In a [multi-cluster](/docs/reference/glossary/#multi-cluster) 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`.