It’s basically a “highlight / stop” list for words in title, stories, author names, etc. nice interface for that, but from my experience not very effective.
Iirc Samuel Mentioned they are working on something better that trains statistics/ML on examples. But at present it’s just a “highlight/stop” list.
newsblur has a 'trainer' feature where you can train it to hide certain topics or authors and highlight others. it doesn't work with every feed though so you'll have to try it out yourself or maybe there are other readers that do something similar