Refresh Rate and Interlacing
In order to maintain a stable image, the electron beam must sweep the entire surface of the screen and then return to redraw it a number of times per second. This process is called Refreshing. Refresh Rate is the number of times per second that the screen is refreshed. It is measured in Hertz (Hz).
Interlacing is a technique of improving the picture quality of a video signal without consuming extra bandwidth. In this technique, each frame is displayed in the passes, In the first pass, the beam sweeps across every other scan line from top to bottom. In the second pass, the beam sweeps out the remaining scan lines.