Property tax, or millage tax, is an ad valorem tax that an owner is required to pay on the value of the property being taxed. Property tax can be defined as "generally, tax imposed by municipalities upon owners of real property within their jurisdiction based on the value of such property." There are three species or types of property: Land, Improvements to Land (immovable manmade objects; i.e., buildings), and Personal (movable manmade objects). Real estate, real property or realty are all terms for the combination of land and improvements. The taxing authority requires and/or performs an appraisal of the monetary value of the property, and tax is assessed in proportion to that value. Forms of property tax used vary between countries and jurisdictions.

The special assessment tax may often be confused with the property tax. These are two distinct forms of taxation: one (ad valorem tax) relies upon the fair market value of the property being taxed for justification, and the other (special assessment) relies upon a special enhancement called a "benefit" for its justification.

The property tax rate is often given as a percentage. It may also be expressed as a permille (amount of tax per thousand currency units of property value), which is also known as a millage rate or mill levy. (A mill is also one-thousandth of a currency unit.) To calculate the property tax, the authority will multiply the assessed value of the property by the mill rate and then divide by 1,000. For example, a property with an assessed value of US $50,000 located in a municipality with a mill rate of 20 mills would have a property tax bill of US $1,000 per year. In more familiar terms, dividing the mills by 10 (moving the decimal point to the left by one) yields the percentage rate – 20 mills = 2.0%. Symbolically, 20‰ = 2% – cancel a '0'.