This is any type of media, usually referencing images or video that can grow and shrink within the space available. This could also apply to a music/audio player. There are no set heights or widths, the media changes size as is appropriate on the page.
Quote:
There’s an awful lot of conflating “design” and “aesthetics” that happens whenever this debate comes up. I’d urge everyone to be clear which it is they’re actually talking about. — David Sleight