A search engine is primarily used for searches of the world wide web through a specific automated web crawler; many search engine companies have also become large web portals, including Google and Yahoo.

A BitTorrent search engine, on the other hand, is geared toward web-based searches of active .torrent files. Many websites also have search engines which allow one to peruse through available torrents that have been indexed by that site's crawler.

Also, like normal search engines, BT search engines can be embedded into the search bar at the top right hand corner of any modern web browser.

From BitTorrent Wiki, a Wikia wiki.