doc: update the glossary with new namespace re-write

Author: Shabirmean

content/en/docs/reference/glossary/namespace.md

@@ -10,9 +10,9 @@ aka:
 tags:
 - fundamental
 ---
- An abstraction used by Kubernetes to support multiple virtual clusters on the same physical {{< glossary_tooltip text="cluster" term_id="cluster" >}}.
+ An abstraction used by Kubernetes to support isolation of groups of resources within a single {{< glossary_tooltip text="cluster" term_id="cluster" >}}.
 
 <!--more--> 
 
-Namespaces are used to organize objects in a cluster and provide a way to divide cluster resources. Names of resources need to be unique within a namespace, but not across namespaces.
+Namespaces are used to organize objects in a cluster and provide a way to divide cluster resources. Names of resources need to be unique within a namespace, but not across namespaces. Namespace-based scoping is applicable only for namespaced objects _(e.g. Deployments, Services, etc)_ and not for cluster-wide objects _(e.g. StorageClass, Nodes, PersistentVolumes, etc)_.