Oricon is famous for its charts and rankings in the Japanese media world. A 'oricon light novel' might refer to a light novel that is listed on Oricon's sales charts for books. These light novels could be part of a large collection of works that are popular among Japanese readers. For example, if a light novel has a really high ranking on Oricon's book charts, it means that it has sold a large number of copies and is likely to be a very popular title among fans of the light novel genre.
I'm not sure specifically which 'oricon light novels' are currently the most popular as it can change over time. But some well - known light novels in general include 'Sword Art Online'. It's a very popular series that has elements of virtual reality and adventure, and it might be among those ranked by Oricon.