Refresh rate is how many times a video panel refreshes per second. This is measured in hertz, and it is closely tied to the frame rate. When the HDMI source and sink are out of sync, you get an effect called “frame tearing”. It is caused by the HDMI sink trying to show more than one frame simultaneously when the source is not ready. Variable Refresh Rate (VRR) enables the source to display the image at the moment it is rendered for more fluid and better detailed video play, and for reducing or eliminating lag, stutter and "frame tearing".