Variable refresh rate
Also called VRR · G-Sync · FreeSync · adaptive sync
Variable refresh rate lets a monitor wait for each new frame instead of refreshing on a fixed clock. G-Sync and FreeSync are the common brand names and both prevent tearing without the delay of V-Sync.
When frame intervals vary widely the refresh rate test reports that variable refresh is probably active. In that case the number it shows is an average rather than the panel maximum.
In practice
Variable refresh is one of the biggest improvements to gaming smoothness in recent years. It removes tearing without the delay of V-Sync and keeps motion smooth when frame rates fluctuate. Its side effects are flicker on some panels when frame rates swing widely and reduced benefit below the monitor’s minimum refresh rate.
How to check
Turn variable refresh on in both the monitor menu and the graphics driver. Then run the refresh rate test. Widely varying frame intervals usually mean variable refresh is active. If you see flicker in dark scenes or loading screens, cap your frame rate a few frames below the refresh rate.