It is the distance between two pixels. It mainly depends on the distance of the viewer. Usually the concept of dot pitch is used for outdoor screens, such as P6, P7.62, P8, P10, P12, P16, P20, etc., in millimeters.
The viewing distance of outdoor screens is generally within 30 meters, and modules no larger than P16 (16mm) are used. The denser the dot pitch, the finer the strokes of the characters displayed. The more pixels per unit area, the more expensive the display cost.