In SharePoint 2013, A list has few items and to each item few tasks are attached. Each task is associated with a workflow. But when a task is deleted the corresponding workflow to the deleted item is still running. How to retrieve such orphaned workflows and find the total count of such workflows in the site.
Finding orphaned workflows is difficult, you can check listed workflows above or check it in Content Database. I strongly don't recommend to work in database, but here is short example.
You can remove orphaned workflows through Workflow Manager. Example here.