Orphaned workflows are workflow tasks and those associated items which have been deleted but sharepoint still keeps a tally of the number of workflow instances running.
i remember in MOSS 2007 that we had to write a script in order to remove Orphaned workflows ....
Not anymore and SharePoint 2010 has made it so much easier ....
In order for the orphaned workflows to be deleted all that is needed to be done is to EMPTY the Recycle bins at the SITE level and then at the SITE COLLECTION level.
and presto ... the orphaned workflows have been removed.