What does the so-called outsole mean in the camera? Is it the difference between SLR and card machine?

I don't know whether you read this statement online or in a book, but I think:

"Bottom"-should come from the size of the film negative.

What we use most often is that the width of the film negative is 35mm. You can watch old movies at home.

There are smaller and larger negatives (rarely seen)

In the digital age, photosensitive elements (CCD or CMOS) have replaced negative films, but there are also different sizes. Outsole and outsole should refer to the size of film negative or CCD/COMS.

In addition, the essential difference between SLR and card is not the bottom. This is the way to observe.

Single-lens reflex camera (this can be checked, there are many explanations and pictures)

Card-the body is relatively small and as thin as a card, hence the name.

Add one more thing:

The size of the "bottom" will determine the viewing angle and the ability to record details (just like two cups with the same height, the larger the bottom area, the more water will be held), so many professional photographers will use the so-called "bottom".

The "outsole" camera ensures that the picture still has good clarity and details when it is put into a large size.

I hope this helps.