How is the search score and search relevance computed?

Kentico uses the Lucene.Net search engine, and the results calculation is rather complex.
Below are some links, which shows how it is done:

Lucene.Net scoring and it is about Vector space model in combination with Standard Boolean model.

As you can see, this logic is fairly complex.  However, the logic also depends on the search index settings, as well as any search filters or search syntax.