Let's start off with learning how a television set works. CRT (cathode ray tube) television sets that we or our parents grew up with displayed a picture via a gun shooting a stream of electrons across the screen, starting at the top of the screen and moving down to the bottom, in lines from left to right. The phosphors that coated the screen glowed as they were hit by the stream of electrons. Since the early TV sets couldn't show the entire picture on the screen without the top of the image fading by the time the bottom was visible, manufacturers developed a system in which half of the lines of the display were refreshed each cycle, while the alternate lines were refreshed the next cycle. This is called interlacing, and that's what the "i" in 1,080i refers to. When using interlaced TV, the screen is fully refreshed after each second cycle.
The 1080 in 1080i refers to the resolution of the TV set. While the old CRT television sets had 576 horizon lines, the new digital high-definition (HD) TV sets boast 1080 lines that make up the image displayed, thereby giving a higher resolution, so digital pictures are four times sharper and clearer than analog ones. Specifically, 1080i TV sets are very good for watching wildlife shows or documentaries, but you may find that 1080p (high-definition TV sets that use a progressive, not interlaced, display) are better for high-action viewing, such as sports events.
1080i HD television has a resolution of 1,920 x 1,080 pixels and gives a very detailed picture. You'll notice that it has five times as many pixels as the standard 720 x 576 pixels. While the 1080p is currently thought of as the best HD TV around, the difference in price, how large a television screen you want, and how close you sit to the screen can make a difference in your viewing experience.