Definitions for "Cost overrun"
(or underrun): A net change in the contractual amount over (under) that contemplated by a contract target price (FFP type), or estimated cost (cost type), due to the contractor’s actual costs being over (under) target or anticipated contract costs, but not attributable to any other cause of cost growth (e.g., quantity changes, engineering changes, economic changes, or changes in estimates of program project costs).
excess of cost over budget; "the cost overrun necessitated an additional allocation of funds in the budget"
The amount of money expended or required over and above budgeted costs in a construction project, including for such items as labor, interest, materials, etc.