Pixel, an abbreviation for picture element, is a cluster of LEDs that make up the individual dots. In real fullcolor solution it has 3 leds in one pixel (1red 1green 1blue) and in virtual fullcolor solution it has 4 leds in one pixel (2red 1green 1blue).
Pixel Pitch is the distance measured in millimeters between the center of two pixels on a display. Pixel pitches for indoor LED screens include 4mm, 5mm, 6mm, 7.62mm, 8mm, 10mm. Pixel pitches for outdoor LED screens include 10mm, 12mm, 16mm, 20mm, 25mm and etc.
The resolution of a LED display is defined by the number of pixels contained in each square meter, in short, resolution = horizontal pixels x vertical pixels. A screen with a smaller pixel pitch will have a higher resolutioin than a same sized one with a larger pixel pitch.