Securing the Cube - Expert Cube Development with SSAS Multidimensional Models - page 271

Here's a visual representation of what this means when the Employees are shown in
the context of the parent/child relationship:
In the screenshot, the dark gray cells show where security User has been explicitly
granted access to an Employee; the light gray cells show where a User has been
granted access to an Employee indirectly, through being granted access to one of the
Employee's ancestors. We can see, for example, that Alberto has access to Amy E.
Alberts and so gets full access to that member's children; he also has access to Garret
R. Vargas but not to that member's parent or siblings.