Video Basics: Concepts
Movies, or motion pictures, were invented around 1870. Through the early 20th century, various improvements were made such as color and the addition of a sound track to the photographic print, but fundamentally the principle remained the same. If a series of sequential pictures (or frames) showing movement is flashed before your eyes fast enough, something called "persistence of vision" will trick your brain into seeing continuous movement, even though there is a brief flash of blankness between each picture.
Video, or television (the electronic version of motion pictures) invented in the 1940's, works the same way, but each picture is painted (or scanned) on the screen (very fast) one line at a time from side to side. Actually every other line in two "interlaced" fields come together to make one video frame. Televisions and tube computer monitors still use a scanning "electron gun" to make each line. Modern flat-screen digital monitors have been a huge advance, making possible many improvements, but fundamentally from camera to screen, a video picture is still composed of scan lines.
Now we consider individual positions on each line and call them "pixels". The size of each pixel is the "resolution" of the picture. Smaller pixels make for higher (better) resolution, or more pixels per inch. In order to put more pixels on the screen you need more lines. If you don't want the picture to go out of shape, you also need to scan faster to increase the number of pixels on each line.
Actually, it gets a lot more complicated than that, but this is the Basics area, so let's save the tricky technical details for the intermediate and pro sections.
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