Define retracing, vertical retracing as well as horizontal

Question

What do you mean by retracing? Define vertical retracing as well as horizontal? 

Answer 1

The electron beam returns to left side of screen to begin displaying next scan line at the end of every scan line. Then it return to left of the screen, after refreshing each of the scan line it is known as horizontal retrace. Electron beam returns to top left corner of screen at the end of each frame, to begin the next frame it is known as vertical retrace.