In general terms, it should be a visual representation of the pieces and how they connect.
I did this (below image) once for a project where nobody seemed to be understanding the setup (main data flow / backup data flow).
For Premium there is no "one size fits all" architecture... but if you listen to their requirements, it's easy enough to make something like this for their needs (e.g. showing WAN links and where to put a terminal server...) using PowerPoint.

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Kevin Moyes
Technical Systems Analyst
Munjal White Consulting Co.
Toronto ON
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