A tax that is assessed on property such as real estate and in some cases personal property such as cars or boats. The assessed valuation of property tax often is based on a rate called mils (also spelled mills), which is the dollar amount of tax that is paid on $1,000 of assessed value. Each governmental unit, such as a city or county government or a school district, receives the payments from a certain number of mils. Property taxes are assessed by city and county governments, not by the federal government.