This is the change in the total cost of an item that occurs when the quantity produced changes by one unit.

The correct answer is: "marginal cost".

The marginal cost of production is defined as the increase in total production costs experienced when an extra unit of output is manufactured. Such increase includes the cost of the extra factors of production that had been dedicated to elaborate the extra unit.

Marginal cost includes variable types of cost, those that change depending on the level of production (such as the amount of raw materials employed) but not by fixed costs that do not vary depending on the level of output (such as the rent paid for the building where the production is undertaken, that is a fixed number).