Market value, assessed value, taxable value
Market value is what the property would sell for. The assessment ratio is the share of it the county taxes: some states assess at 100%, others at a fraction, and the ratio is often the reason a bill looks lower or higher than the rate suggests.
Exemptions then come off the assessed value rather than the market value. A $25,000 homestead exemption on a property assessed at $320,000 leaves $295,000 taxable, which is a different number from $25,000 of market value and is why exemption amounts cannot be compared across states without this step.