2d spritesheets for game development are often distributed as a PNG image, sometimes with a separate JSON or XML metadata document describing the layout, including any animation sequences within the sheet. Sometimes there is no metadata document and you have to work it out and manually write custom code to chop up the spritesheet and reference the sprites you want.
I think it would be good if it became standard practice to distribute spritesheet PNGs with the metadata inline inside a PNG "chunk" so the whole thing is self-contained. That way artists can just distribute one file, and tools and libraries can read the metadata directly from it. That's what this spec/standard is about.
The linked page proposes a standard, describes the technique's details, and provides an online tool for inlining metadata into the sheet. Hope it's useful!