The term "additional cost" refers to any expenses that are not included in the original price or estimate of a product, service, or project. These costs can include things like taxes, fees, shipping and handling charges, insurance premiums, permits, licensing fees, and other miscellaneous expenditures that may be necessary to complete a task or fulfill an obligation. The phrase is often used in business transactions, contracts, and proposals to indicate any extra costs that might be incurred beyond the initial quote or estimate.