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A square pixel has a 1:1 aspect ratio (width is the same as the height). Any other rectangular pixel with widths different than their heights would be considered "non-square".

F.ex. in case of a "4:3 720x480" frame… a quick test: 720/4=180 and 480/3=160… 180 vs. 160… different results… which means the pixels for this frame are not square, just rectangular. Alternatively 720/480 vs. 4/3 works too, of course.

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Again I think you're talking about pixel aspect ratios instead, and not physically non-square pixels, which would be display-dependent. OP only said "square pixels" but then only talked about aspect ratios, hence my confusion.

Dots on a crt are not pixels. Their shape depends on the shadow mask.

OP quoted “non-square pixels” from the article, which is talking about pixel aspect ratios, i.e., width vs height. The implicit alternative to square in this context is rectangular, we’re not talking about circular or other non-rectangular shapes. Whenever the display aspect ratio is different than the storage or format aspect ratio, that means the pixels have to be non-square. For example, if a DVD image is stored at 720x480 and displayed at 4:3, the pixel aspect ratio would have to be 8:9 to make it work out: (720x8)/(480x9)==4/3. I believe with NTSC, DVDs drop a few pixels off the sides and use 704x480 and a pixel aspect ratio of 10:11.

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