* To avoid confusion between the photo search feature on your own website, and external internet search engines like Google, Yahoo, etc., from now on I will refer to all the external internet search engines just as "Google".
The WideRange Galleries software enables you to build an index of suggested search terms for the onsite photo search feature - like a glossary of your photos. This is a powerful and useful feature because it enables you to present your photos in an alternate structure than the normal gallery structure. Some photographers chose to include only their best photos in their galleries, but they can upload many more photos (such as stock photos) that are only accessible via the photo search. By setting up a search index, you can create a list of search terms that will provide easy access to all those searchable images, without making the customers guess the search terms.
Not only is the search index useful for potential stock customers, but those search result pages will eventually get indexed by Google. Without the search index, no search results will ever by indexed because Google can't guess what to enter in the Search box. By creating a search index, you are creating a list of links to actual pages that Google's spiders can crawl and index. This is why each search tag you enter gets Page Keywords and Page descriptions - because they are actual pages on your website.
You can see an example of a search index here.