It's a namespace that contains HTML elements. Pretty obvious choice for the name. Presumably there would be "svg:" for SVG.
It seems the author's fatal mistake was not assigning the "html:" URI to the root namespace since everyone here is so caught up on "HUR DUR HTML:HTML THAT'S SO DUMB LOL XML SUCKS".
It seems the author's fatal mistake was not assigning the "html:" URI to the root namespace since everyone here is so caught up on "HUR DUR HTML:HTML THAT'S SO DUMB LOL XML SUCKS".