Generally speaking, tax exemptions are used to reduce or eliminate the amount an individual is required to pay in taxes, similar to a tax deduction. Exemptions help determine an individuals 'taxable income' (in other words, the income that can be taxed by the government).
Property tax exemptions are specific to the property's local state, county or city and have to be located and applied for by an individual property owner (or their tax professional), as these exemptions are not automatic (i.e. the government will not automatically apply them nor automatically tell an individual if they qualify for one).
Property tax exemptions can come in the form of homestead exemptions, disabled homeowners, senior homeowners, military veterans, renovations, energy incentives, and other exemptions.