Farmland assessment
A preferential assessment program for qualifying actively devoted agricultural or horticultural land, subject to statutory requirements and possible rollback taxes after disqualifying changes in use.
New Jersey example
A low farmland assessment should not be treated as ordinary residential market-value evidence.
Official source
https://www.nj.gov/treasury/taxation/lpt/farmlandassessment.shtml
This is a plain-English summary. Rules and dollar amounts change, so check the official source or a professional before you file or sign anything.