Pronounced (in a Pittsburgh accent) DAAAAAAAAYYYYYNNNNAAAAAAA
Is short for Drush Assign Author Nodes to Another Author
This was created in the even that you bulk delete a user from a bunch of sites (say an employee that no longer works for you). You can run drush ucan which will remove the user from the system and give all their content to anonymous. Well, there's no good way of assigning those nodes to someone else via drush.