VIX Ref is the price of the VIX at the time the SpotGamma data was calculated. 

Why does VIX Ref matter?

A large change in VIX may mean that implied volatility has shifted significantly. 

How to use VIX Ref

A higher VIX likely means options market makers have added short hedges which adds market selling pressure. A lower implied volatility means options market makers may add buying pressure.