REFRESH RATE is a measure of how many times per second an image is redrawn on the screen. It is measured in Hertz (Hz) .For example, a refresh rate of 1920Hz means the image is refreshed 1920 times in one second.
Below picture shows the difference of LED screens with low refresh & high refresh rate. Flickering will occur if the refresh rate is too low.
Generally, common RGB LED displays require a 1920Hz refresh rate. A high speed action movie or content displayed on a RGB LED wall will require more than 2550Hz refresh rate is.