An area in front of a coalface where no props are placed, so as to leave access for a mechanical conveyor, the roof being supported by cantilever bars; the system of supporting a roof in this way.
Origin
1950s.
Definition of prop-free front in US English:
prop-free front
noun
Mining
An area in front of a coalface where no props are placed, so as to leave access for a mechanical conveyor, the roof being supported by cantilever bars; the system of supporting a roof in this way.