For users with multiple Solr index collections, Solr aliases can help provide federated, sorted search results to make all of the accompanying documents more manageable to search through. They are created in Workflow Designer and then appear as a selectable index value in the Search App.
The results can then be queried, refined, and sorted based upon the settings you implement, and bulk actions can also be applied.
To learn more about Solr aliases, see the Apache Solr Reference Guide or the Workflow Designer Help.