A refresh rate is simply the amount of images shown on a screen per second. The general specs one will see for it will be 60 Hz, or 120 Hz. It is measured in Hz which is a measurement of frequency. In this case, 60 Hz will denote that the frequency at which pictures are shown for that screen is 60 images per second. It is a common property of monitors or televisions and it will dictate the maximum frames per second (fps) that the system is able to put out. For example, having a game running at 128 fps will show no improvements if the screen it's being played on has a refresh rate of 60 Hz. In that case, the screen can't keep up with how fast the game wants to show images, so it will default at 60 fps as it's fastest speed.