What does the px in the photo mean?

Px in the photo is the abbreviation of pixel, which is a pixel, not a unit of length in nature. Px is the smallest point in the picture, and the bitmap is made up of these points. 1024px is1024px, which can be seen in the Settings of the windows desktop properties. If it is 1024×768, it means that there are 1024 points in the horizontal direction and 768 points in the vertical direction. If the point is small, the picture is clear, which is called "high resolution", otherwise it is "low resolution". Therefore, the size of the pixel will "change", which is the so-called "relative length".