A query block is a section of your document that is linked to a query in Team Foundation Server. Using a query block you can keep the content of your document up-to-date with the latest results of your query. If work items are added or removed from the query, simply refresh the query block to see the latest results.
Query blocks support work item relationships. Different templates can be applied to parent and child work items. Additionally, different templates can be applied to work item types. For example, a parent work item type of “Product Backlog Item” can have nested “Tasks” and “Test Cases” under it in the document.