Quote from the guide:
” A simple explanation for how TV works is that a transmission signal sends information to your TV.
The information tells the TV what the picture is supposed to look like. Once received, the TV paints that picture onto the screen pixel by pixel, forming horizontal rows, called ‘scan lines,’ across the screen. The TV continues to paint and re-paint these scan lines multiple times every second. This refreshing of the scan lines happens so fast that the human eye perceives the changing picture as fluid movement.
Devices that utilize interlaced scanning paint half of the scan lines (referred to as a field) and then paint the second half. Each field is updated 60 times per second. And a frame, made up of the two fields, is completely refreshed 30 times per second. While interlacing works well on smaller sets, on the bigger TV screens that are out today, the refreshing process may be visible to the eye, so that some people notice a perceptible flickering. “
Read the full guide at eCoustics