Definition
PRECISION OBSTACLE FREE ZONE (POFZ)
An 800 foot wide by 200 foot long area centered on the runway centerline adjacent to the threshold designed to protect aircraft flying precision approaches from ground vehicles and other aircraft when ceiling is less than 250 feet or visibility is less than 3/4 statute mile (or runway visual range below 4,000 feet.)
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).