What does it mean that the longest side of a photo in photography is * * * pixels?

The ratio of ordinary photos is 4:3 and 3:2.

But sometimes because the film is shot vertically, the long side becomes short after rotation. Therefore, expressions such as "width" and "height" will obviously cause misunderstanding. To clarify the concept,

The longest side refers to the width and height of the photo, and the longer side can be understood as the side with more pixels.

The longest side of a 500W pixel is generally 2560 pixels.