IMO A "quality" article from a human perspective is one that you as the reader would find really interesting, useful and one that you would want to share. If it is interesting and useful, you would want to share it with your friends, aka link to it on social media or put a link on your own website.
So if this is what a human finds quality, then this is what Google will be trying to emulate.
Therefore from an SEO perspective (aka a computer algorithm's perspective) a quality article would have 1000-1500+ words, it would not be just be a block of text, it would have paragraphs, spacing between text, images, gifs, videos, H1, H2 etc, dot points, bolded / italic text, graphs, tables etc. It would also have links going to the page it is on, from social media, and from other relevant authority websites. The traffic to the article would spend a long time on the page and not bounce back, probably click a link in the article out to something or close the tab.
And of course you can achieve this with White, Grey or Blackhat methods.