Understanding Pixel Differences in Graphics and Video
The term square pixel actually refers to the horizontal and vertical distance from a pixel
to its neighbors. With a square pixel, the distance is the same in both directions. This
distance is a function of the sampling rates, both horizontal and vertical, and the aspect
ratio the graphic will be displayed in. Given the right aspect ratio, virtually any combination
of horizontal and vertical sampling rates could produce square pixels.
Computer graphics programs are optimized to work with square pixels: When you draw
a square, it has the same number of pixels in all four of its sides and looks like a square
on the display.
Unfortunately, SD video is different.