Plain English Meaning
VREF is the speed a pilot aims to be flying as the airplane crosses the runway threshold on landing. It is set fast enough to keep a safe margin above the stall, but slow enough to land cleanly.
Full Definition
VREF is the airspeed used as the reference for the final approach to landing, typically defined as 1.3 times the stall speed in the landing configuration (1.3 VS0) at maximum landing weight. It is the target speed crossing the runway threshold in a stabilized approach.
Context Anchor
You see VREF in landing performance data, , and callouts when setting the target speed for the part of a landing.