I expect that they are talking about the way that beauty is portrayed in the media and suchlike. As if different levels of beauty fall along a line (linear). This is uglyness and this is beauty. This feature makes you beautiful, this makes you ugly. Whereas in reality "beauty is in the eye of the beholder", as they say. One person may think someone is ugly, but another person may think they are beautiful. It is subjective. Some people find skinny attractive, some find chubby attractive. Beauty doesn't actually sit on a line from ugly to beautiful. Everyone sees it differently, or at least it's less straightforward. Some people think Brad Pitt or Jennifer Lawrence look amazing, others don't and might prefer someone else.