OtherIndexes
Other indexes probably use the same engine, but contain different indexed material, so either you can experiment with the indexing method checking different kind of pages, or you can hope to get more meaningful results by selecting another one.
I guess indexes are constantly growing, so you can try them from time to time.
Can sombody explain: What is an index in this context?
An Index contains all the information the searchengine knows, and the Crawler crawls that information. So a crawler takes the informations from the websites word by word, and puts it into a database, this is the index.