Interlaced video is the technique of blending two fields of video in order to double the perceived frame rate and reduce flicker without consuming extra bandwidth. These fields are the odd or even scan lines of a video.
When the television was first introduced, interlacing was necessary since early sets could not keep persistent images on the phosphor long enough to scan progressively from top to bottom without flickering. By interlacing, each field could stay on screen long enough to simulate motion.
For example: At 30 frames per second, when these scan lines are alternated, 60 fields per second are produced, creating an intermediate frame between each full frame of video that is a blend of the prior frame’s odd scan lines with the later frame’s even scan lines.
While this method effectively reduces flicker, it also produces unwanted artifacts on the intermediate frames called interline twittering.
Displays that are interlaced are indicated with an “i” after the pixel resolution.