This is the measurement used to determine how sharp the display of a CRT (Cathode Ray Tube) monitor is. It is measured in millimeters and the smaller the number, the finer the picture. Most CRT monitors will have a dot pitch between 0.25 and 0.28. However, some large presentation monitors have dot pitches from 0.30 to 0.50 (which would make for really fuzzy images on a standard 17" desktop monitor). The difference between a "dot" (as in dot pitch) and a pixel is that a pixel is mapped onto the dots on the screen. When the monitor is set to lower resolutions, one pixel encompasses multiple dots. So pixels are typically larger than the "dots" on the actual screen.
In a CRT display with a shadow mask, the dot pitch is measured as the distance between the holes of the shadow mask, again in millimeters. "So what's a shadow mask?" you ask. It's basically a metal screen full of holes where three electron beams (red, green, and blue) pass through. These beams focus to a single point on the tube's phosphor surface. Thousands of these points make up the images on your screen. Neat, huh? In a CRT display that uses an aperture grill (like a Sony Trinitron monitor), the dot pitch is measured by the distance between adjacent slots where electron beams of the same color pass through.
Updated: June 1, 2006