No idea what Neeva does, but from what NoGoogle said I'm guessing it's some sort of AI thing?
So (as an example) if you upvote StackOverflow, and many people who've upvoted StackOverflow also upvote GitHub, then it can automatically start showing you more GitHub results as well. (Looking at it one way, this is effectively some kind of collective preference/decision-making rather than an individual one. I think the intention here is different though; it's to have the search engine guess your preferences without you having to tell it).
Alternatively it might be done through some sort of "similarity" ranking, so if the algorithm finds out (through some other means) that Medium and Newsbreak are similar, downvoting Medium will also show you less Newsbreak posts.
Personally, I'm a little concerned that this would again introduce some sort of algorithmic black-box/filter-bubble which the user has no control over. But perhaps it'll work out if you adjust the strengths properly (eg. upvoting StackOverflow also shows more of GitHub, but I can override that by downvoting GitHub. The catch is to make sure downvoting GitHub doesn't also downvote StackOverflow by the same amount, because then there'd be no easy way to disentangle one from the other!).
