Update docs/reference/glossary/rbac.md

Author: ym1024

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

@@ -15,5 +15,10 @@ tags:
 
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-RBAC utilizes *roles*, which contain permission rules, and *role bindings*, which grant the permissions defined in a role to a set of users.
+RBAC utilizes four kinds of Kubernetes objects:
+* **Role**: Defines permission rules in a specific namespace.
+* **ClusterRole**: Defines permission rules cluster-wide.
+* **RoleBinding**: Grants the permissions defined in a role to a set of users in a specific namespace.
+* **ClusterRoleBinding**: Grants the permissions defined in a role to a set of users cluster-wide.
 
+For more information, see [RBAC](/docs/reference/access-authn-authz/rbac/).