Plain English Meaning

It's a visibility measurement taken from a device sitting next to the middle of the runway, telling you how far you'd be able to see down the runway from that point.

Full Definition

A Runway Visual Range value reported from a sensor located near the midpoint of the runway, indicating the horizontal distance a pilot can expect to see down the runway from that midfield position. It supplements the touchdown zone RVR and, where installed, the rollout RVR, and is a controlling value for certain low-visibility approach operations such as CAT II and CAT III approaches.