Cost of vacancy
Also known as: cost of a vacancy
Cost of vacancy is the financial impact of leaving a role unfilled: the lost output, revenue, and momentum the position would otherwise produce. For a key role it often runs to roughly double the salary, which is why an empty seat is rarely the cheaper option.
An unfilled seat feels free because no salary is going out, but the work it would do is not getting done, and that gap usually costs well more than the wage saved.
Weighed against time-to-fill and quality of hire, the cost of vacancy is usually the strongest case for moving deliberately but not slowly: protect the bar, but do not let a critical role drift for months.