Query is a request for information to the issues database.
When you start JIRA Client for the first time, it already contains a set of default queries in Sample Queries folder in the Navigation Area.
Sub-query filters the results of its parent query by type (for example, bug, new feature, task, and improvement), priority (blocker, critical, major, or trivial), and other parameters. Picture above shows a distribution of issues by their priority.
You can create your own queries by, for example, pressing the New Query button toolbar and setting any combination of AND, OR, and NOT operators in the Create Query dialog.on the