What is an indirect tax where a specific amount is added to the selling price of each unit?

The concept behind a tax that involves adding a specific amount to the selling price of each unit is a flat rate tax. This type of tax applies a fixed monetary amount per unit sold, regardless of the selling price, so the tax burden is directly proportional to the number of units sold, rather than the price of each unit.

In the context of indirect taxes, a flat rate tax uniquely impacts consumers because it simplifies the calculation of tax owed on goods or services. For example, if each unit sold incurs a tax of $2, every product sold will have an additional $2 added to its price regardless of its value.

In contrast, an ad valorem tax is based on the value of the good or service, meaning that the tax amount changes in accordance with the price. Variable costs refer to costs that vary with the level of output, which is different from tax definitions. Thus, flat rate tax effectively aligns with the description provided in the question, as it encapsulates the idea of a specific amount added per unit.