In terms of web design, it usually expresses advanced adapting to different breakpoints/screen sizes, but it's difficult to draw the line where something stops being a regular responsive design and starts being artistically directed.

In the context of this article, it's about cropping images (e.g. you could have a full-body shot of the company CEO on the desktop version of your page and then just crop the face for mobile). One can already achieve the same effect in modern browsers using the picture element, although the cropped versions of images need to be prepared in advance.

I took it to mean the way you can focus or highlight parts of a visual element, image, whatever, by cropping or repositioning it.