Final answer:
The term that describes the level of taxes imposed on the tax base and expressed as a percentage is the tax rate. Tax rate, tax deduction, tax credit, and tax exemption are distinct tax terms with different implications for the taxpayer.
Step-by-step explanation:
The term that describes the level of taxes imposed on the tax base and is usually expressed as a percentage is known as the tax rate. A tax rate determines how much tax an individual or a corporation owes to the government relative to the taxable income or other tax base. It is distinct from a tax deduction, which lowers the total income subject to tax, or a tax credit, which directly reduces the total tax bill. A tax exemption, on the other hand, fully excludes certain income or transactions from being taxed at all.