The millage rate is the amount per $1,000 used to calculate taxes on property. A mill is a thousandth of a dollar. So 1/10th of a penny.
LET’S BREAK DOWN MILLAGE RATE!
For example, if the tax rate is 50 mills , the annual tax is 5 cents per dollar of value; 5% of the value – which is $10,000 for a $200,000 property.
As stated on Investopedia, The term is derived from the root word mill, which means “thousand.” Millage rates are often expressed mathematically with the symbol %o, as in 1%o, which is one part per thousand, or 0.1%. Millage rates for individual properties are usually found on the property deed itself. Frequently, these taxes are labeled in “mills,” with one mill representing $1 in tax per $1,000 in tax-assessed value.
Here is a nice explainer video: