Updating glossary definition to include use case (#517)

Co-authored-by: Ashley Brown <[email protected]>

Author: mdb-ashley

source/reference/glossary.txt

@@ -764,7 +764,9 @@ Glossary
       query plan. See :ref:`read-operations-query-optimization`.
 
    query shape
-      A combination of query predicate, sort, and projection.
+      A combination of query predicate, sort, projection, and
+      :doc:`collation </reference/collation>`. The query shape allows MongoDB 
+      to identify logically equivalent queries and analyze their performance.
 
       For the query predicate, only the structure of the predicate,
       including the field names, are significant; the values in the