tl;dr is that those are different approaches to weighting documents in order to return the most relevant ones for a query. For an intro to the problem space, s

tl;dr is that those are different approaches to weighting documents in order to return the most relevant ones for a query. For an intro to the problem space, see https://opensourceconnections.com/blog/2014/06/10/what-is-search-relevancy/ https://opensourceconnections.com/blog/2014/06/10/what-is-se... If you want a lot more detail, check out the book Relevant Search. https://www.manning.com/books/relevant-search https://www.manning.com/books/relevant-search