What's the difference between an abatement and an exemption?

An exemption is a discharge from the obligation to pay all or part of a real estate tax based on certain age, income, military, or disability status as set forth by the Commonwealth of Massachusetts.  
         Exemptions are available for seniors, low-income seniors, surviving spouse or surviving minor child, veterans with disabilities, and blind persons.

         An abatement happens as a result of an adjustment that lowers a property valuation after the actual (not preliminary) tax bill has been issued.