Which term defines total tax paid divided by total taxable income as a percentage?

The correct term that defines total tax paid divided by total taxable income as a percentage is the Average Tax Rate. This measure provides insight into the overall burden of taxation on an individual's or entity's income.

The Average Tax Rate is calculated by taking the total taxes owed and dividing it by the total taxable income, then multiplying by 100 to express it as a percentage. This rate gives a clear representation of how much of a person's or business's income is going toward taxes on average, regardless of different tax brackets or rates that apply to portions of income.

In contrast, the Marginal Tax Rate refers to the tax rate applied to the next dollar of income earned, focusing on the tax applied at specific income levels rather than the overall tax burden. The Effective Tax Rate is often used to describe the rate that factors in all tax liabilities, including credits and deductions, but it is not solely defined as total tax divided by taxable income. The Proportional Tax Rate indicates a tax system where everyone pays the same percentage of their income regardless of income level, which doesn't apply universally to all tax systems.

Therefore, the Average Tax Rate is the most appropriate term for the description given in the question.