Understanding query rules
Without any custom code, you can help searches respond to the intent of your users by creating query rules. In a query rule, you specify conditions and correlated actions. When a query meets the conditions, the search system performs the actions to improve the relevance of the search results.
For example, you might specify a condition that checks whether the query matches a term in a SharePoint term set, or another condition that checks whether the query is frequently performed on a particular search vertical in your search system, such as Videos.
A query rule can specify the following three types of actions:
Add Promoted Results (formerly called Best Bets) that appear above ranked results. For example, for the query "sick leave", a query rule could specify a particular Promoted Result, such as a link to a site that has a statement of company policy regarding time off work.
Add one or more groups of results, called result blocks. A result block contains a small subset of results that are related to a query in a particular way. Like individual results, you can promote a result block or rank it with other search results. For example, for a query that contains “Fabrikam sales report”, a query rule might use a taxonomy dictionary to recognize “Fabrikam” as a customer, and then display a result block with pertinent results about Fabrikam from your customer relationship management (CRM) system.
Change the ranking of results. For example, for a query that contains “download toolbox”, a query rule could recognize the word “download” as an action term and boost search results that point to a particular download site on your intranet.
For more information, see:
SharePoint Online: Manage query rules (Office.com)
SharePoint Server 2013: Manage query rules in SharePoint Server 2013 (TechNet)