The effective tax rate is the rate at which your taxes are calculated. It is arrived at through a complex mathematical formula. The goal of the formula is to prevent changing the tax revenue generated by a political subdivision simply because the value of property has increased or decreased due to market conditions.
The thought process behind this is that when you vote on a levy, you are voting to give the political subdivision a certain amount of money. If values of real estate change due to market conditions, the taxes should not necessarily change with them. In other words, just because your property value went up 10% does not mean it costs 10% more to provide fire service to your property.