Clarify an ambiguous behavior description

Author: dimitri-furman

docs/relational-databases/indexes/reorganize-and-rebuild-indexes.md

@@ -4,7 +4,7 @@ description: This article describes index maintenance concepts, and a recommende
 author: dimitri-furman
 ms.author: dfurman
 ms.reviewer: mikeray
-ms.date: 09/18/2024
+ms.date: 10/11/2024
 ms.service: sql
 ms.subservice: table-view-index
 ms.topic: conceptual
@@ -55,7 +55,7 @@ What is **page density** (also known as page fullness) and how it impacts perfor
 
 - Each [page](../pages-and-extents-architecture-guide.md#pages) in the database can contain a variable number of rows. If rows take all space on a page, page density is 100%. If a page is empty, page density is 0%. If a page with 100% density is split in two pages to accommodate a new row, the density of the two new pages is approximately 50%.
 - When page density is low, more pages are required to store the same amount of data. This means that more I/O is necessary to read and write this data, and more memory is necessary to cache this data. When memory is limited, fewer pages required by a query are cached, causing even more disk I/O. Consequently, low page density negatively impacts performance.
-- When [!INCLUDE [ssDE-md](../../includes/ssde-md.md)] adds rows to a page, it will not fill the page fully if the [fill factor](specify-fill-factor-for-an-index.md) for the index is set to a value other than 100 (or 0, which is equivalent in this context). This causes lower page density, and similarly adds I/O overhead and negatively impacts performance.
+- When [!INCLUDE [ssDE-md](../../includes/ssde-md.md)] adds rows to a page during index creation, rebuild, or reorganization, it will not fill the page fully if the [fill factor](specify-fill-factor-for-an-index.md) for the index is set to a value other than 100 (or 0, which is equivalent in this context). This causes lower page density, and similarly adds I/O overhead and negatively impacts performance.
 - Low page density can increase the number of intermediate B-tree levels. This moderately increases CPU and I/O cost of finding leaf level pages in index scans and seeks.
 - When the Query Optimizer compiles a query plan, it considers the cost of I/O needed to read the data required by the query. With low page density, there are more pages to read, therefore the cost of I/O is higher. This can impact query plan choice. For example, as page density decreases over time due to page splits, the optimizer can compile a different plan for the same query, with a different performance and resource consumption profile.