In recruiting, cost-per-vacancy refers to the costs that are automatically incurred as soon as a position remains unfilled.
Often the costs for an unfilled vacancy are higher than the person filled would earn in a year. The reason for this is the loss of potential revenue, frustration and absenteeism of the rest of the team, increased chances that other team members will also quit, and that subject areas are partially left undone, resulting in unfinished projects and customer orders.