How much detail appears in the picture. This is a function of how many pixels are devoted to the picture. The more dots, the finer the detail. As computer and television technology draw closer together, there's a problem with defining resolution. Traditionally the vertical resolution of TV has been expressed in terms of lines. PAL has 576 visible horizontal lines (NTSC has 480). This is easy to understand because these are the scan lines built into the signal. Traditionally TVs don't produce all of these lines because of overscan and because of the Kell Effect. For TV, the horizontal resolution has also traditionally been expressed in terms of lines, in this case vertical ones. This is a fairly subjective judgment based on density of closely spaced lines that can be perceived on a screen. DVDs, deriving from computer technology, are instead expressed in terms of pixels. PAL ones have a vertical resolution of 576 pixels (subject to letter boxing, and 480 for NTSC). They also have a theoretical horizontal resolution of 720 pixels. At least, that is the resolution at which the pictures are encoded on the DVD (both for PAL and NTSC). However the great majority of DVD players do not have digital video outputs. So this horizontal resolution has to be down-converted to a resolution that a TV is capable of handling, typically between 500 and 540. DVD players which incorporate DVI or HDMI outputs are now appearing. These can deliver the full 720 pixels of horizontal resolution.