From https://investinganswers.com/ --

The marginal tax rate is the percentage of tax applied to your income for each tax bracket in which you qualify. In essence, the marginal tax rate is the percentage taken from your next dollar of taxable income above a pre-defined income threshold.

The marginal tax rate includes federal, state and local income taxes, as well as federal payroll and self-employment taxes. This differs from the average tax rate, which is the total tax paid as a percentage of total income earned.