Plain English Meaning
A landing or takeoff surface that is loose, soft, or yielding -- like grass, dirt, sand, mud, or snow -- where the wheels sink in or drag, slowing the airplane down on the ground.
Full Definition
A runway or takeoff/landing surface whose composition causes increased rolling resistance and reduced acceleration during ground operations. Typical soft fields include grass, sand, mud, snow, or wet or rain-soaked turf. Operations on a soft field require specific takeoff and landing techniques to keep aircraft weight off the wheels as much as possible and prevent the airplane from becoming bogged down or nosing over.