Turning is a term used in Erfworld for a unit changing from one side to another. The process is unclear; casters captured in battle, especially after a side is destroyed and they become barbarians, sometimes join their captors, particularly as an alternative to croaking. A unit can apparently turn in the field if properly motivated; of course, Obedience, Loyalty, and Duty all work against this process.
When Jillian was under the influence of Wanda, and would not attack the wounded dwagons, Jaclyn tried to prod her into choosing some course of action, including abandoning the fight or turning to Stanley's side and joining up with the dwagons.
Later, Jillian asked Wanda to turn and join the Royal Crown Coalition.
One Turnamancer called Vanna has displayed skill at Turning. Whether this means all Turnamancers can Turn, or whether only some Turnamancers can Turn, or only that Turnamancer could Turn that turn, hasn't been specified.