The Search API module (http://www.drupal.org/project/search_api) replaces the Drupal core search with a framework that can be used with different kinds of underlying search engines. The search engines exist as third parties independent of the Drupal site and its database.
Thomas Seidl (also known as "drunken monkey") is one of the main contributors to the Search API module. This is how he explained its origins:
"Search API was created in 2010. I was involved in discussions about how to improve Drupal's core search module and turn it into more of a framework for Drupal 8. The problem was that there was no search framework in Drupal and all search-related modules had to include the same boilerplate code over and over. I took the best parts of that discussion and turned them into a contributed module and search framework for Drupal 7."
The Search API module can be extended with other contributed modules to provide very powerful search functionality. Search API also integrates...