The dot pitch specification for a display monitor tells you how sharp the displayed image can be. The dot pitch is measured in millimeters (mm) and a smaller number means a sharper image. In desk top monitors, common dot pitches are .31mm, .28mm, .27mm, .26mm, and .25mm. Personal computer users will usually want a .28mm or finer. Some large monitors for presentation use may have a larger dot pitch (.48mm, for example). Think of the dot specified by the dot pitch as the smallest physical visual component on the display. A pixel is the smallest programmable visual element and maps to the dot if the display is set to its highest resolution. When set to lower resolutions, a pixel encompasses multiple dots.
Technically, in a cathode ray tube (CRT) display with a shadow mask, the dot pitch is the distance between the holes in the shadow mask, measured in millimeters (mm). The shadow mask is a metal screen filled with holes through which the three electron beams pass that focus to a single point on the tube's phosphor surface. In CRTs that use an aperture grill (a slotted form of mask), such as Sony's Trinitron flat-screen technology, the dot pitch is the difference between adjacent slots that pass through an electron beam of the same color.