Define pure marts (#6394)

## What are you changing in this pull request and why?

Closes #6329

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Co-authored-by: Leona B. Campbell <[email protected]>

website/docs/best-practices/how-we-structure/4-marts.md

@@ -26,7 +26,8 @@ models/marts
 
 ✅ **Group by department or area of concern.** If you have fewer than 10 or so marts you may not have much need for subfolders, so as with the intermediate layer, don’t over-optimize too early. If you do find yourself needing to insert more structure and grouping though, use useful business concepts here. In our marts layer, we’re no longer worried about source-conformed data, so grouping by departments (marketing, finance, etc.) is the most common structure at this stage.
 
-✅ **Name by entity.** Use plain English to name the file based on the concept that forms the grain of the mart `customers`, `orders`. Note that for pure marts, there should not be a time dimension (`orders_per_day`) here, that is typically best captured via metrics.
+✅ **Name by entity.** Use plain English to name the file based on the concept that forms the grain of the mart’s `customers`, `orders`. Marts that don't include any time-based rollups (pure marts) should not have a time dimension (`orders_per_day`) here, typically best captured via metrics.
+
 
 ❌ **Build the same concept differently for different teams.** `finance_orders` and `marketing_orders` is typically considered an anti-pattern. There are, as always, exceptions — a common pattern we see is that, finance may have specific needs, for example reporting revenue to the government in a way that diverges from how the company as a whole measures revenue day-to-day. Just make sure that these are clearly designed and understandable as _separate_ concepts, not departmental views on the same concept: `tax_revenue` and `revenue` not `finance_revenue` and `marketing_revenue`.