Final answer:
In flexible budgets, the costs that remain unchanged regardless of output levels are known as fixed costs. These costs, such as rent for a space or the cost of machinery, do not vary with production quantity.
Step-by-step explanation:
In flexible budgets, costs that remain the same regardless of the output levels within the relevant range are fixed costs. Fixed costs include expenses such as the rent on a factory or retail space, where the amount due does not vary with the level of production. They are contrasted with variable costs, which change with the production level, and these costs typically demonstrate diminishing marginal returns.
Fixed costs are a type of sunk cost, meaning the money has already been spent and cannot be recovered. Such costs shouldn't factor into economic decisions about future production or pricing. Examples of fixed costs, in addition to rent, may include the cost of machinery, research and development expenses, and advertising intended to establish a brand.