Spotlight also allows you to search songs in iTunes, email messages in Apple Mail, addresses in Address Book and for other similar functions in Mac OS X programs.
When a word is searched in a Spotlight application, results come up immediately. Some programs even use more than one function of Spotlight. For example Safari uses Spotlight for searching RSS feeds, browsing history and bookmarks.
Some programs do not use Spotlight inside the program but they give ways to highlight a document so that the files could be easily searched with global Spotlight searches. Some programs let you select keywords, which can be used for Spotlight searches later.