In the context of responsive web design, a responsive image is one that's made fluid with the width, height, aspect-ratio, and object-* properties, as part of CSS layouts that change with the viewport size and other media conditions.
But what the HTML Standard is concerned with, and what this article talks about, are the so-called "adaptive images" enabled by the srcset and sizes attributes on <img>, and the <picture> and <source> elements. These HTML features help the browser pick the most appropriate image content for the current environment.
A CSS pixel is defined as the visual angle of one pixel on a device with a device pixel density of 96dpi and a distance from the reader of an arm's length or about 0.0213 degrees.
[
add
]
[
|
|
...
]