Plain English Meaning

It means a pilot can see only 300 feet down the runway. This is the very lowest visibility a specially approved operator is allowed to begin a takeoff in.

Full Definition

A Runway Visual Range (RVR) value of 300 feet, representing the horizontal distance a pilot can see down the runway from the approach end. In OpSpecs, 300 feet RVR is the lowest takeoff minimum authorized for properly equipped operators on runways meeting specific lighting, marking, and surface requirements, and only when the flight crew and aircraft are qualified for that minimum.

Context Anchor

Seen in OpSpecs, low-visibility instrument approach procedures, and that give runway visual range values.