A Story is marked Stale when it is in an active Workflow State and has not been updated within a certain number of days. The “Days Until Stale” setting is set at the Project level; learn how to set or change the Staleness indicator on your Project.
Setting Story Staleness is a way to is a way add a visible indicator to any Story in a Project that hasn’t been worked on recently. If a Story goes Stale, you’ll see an hourglass icon appear on the front of the Story with the number of days since it saw activity. You can also search for Stale stories - learn more about finding Stories that have gone stale.