Wording.

Masonry

A layout where items are arranged in columns of equal width but variable height, each item stacking directly below the shortest column — like brickwork.

Example usage
The image gallery uses a masonry layout so portrait and landscape photos coexist without cropping.
Editor’s note

Masonry works well for content with unpredictable aspect ratios. It breaks down for content that needs to be scanned in order — use a grid instead.