Weighting decides which document gets priority over other documents and appear at the top. In Sphinx, weighting depends on the search mode. Weight can also be referred to as ranking. There are two major parts which are used in weighting functions:
Phrase rank: This is based on the length of Longest Common Subsequence (LCS) of search words between document body and query phrase. This means that the documents in which the queried phrase matches perfectly will have a higher phrase rank and the weight would be equal to the query word counts.
Statistical rank: This is based on BM25 function which takes only the frequency of the queried words into account. So, if a word appears only one time in the whole document then its weight will be low. On the other hand if a word appears a lot in the document then its weight will be higher. The BM25 weight is a floating point number between 0 and 1.