The desktop search function in Mac OS X, starting with Version 10.4. Spotlight lets users search for data located within almost any type of file stored in the computer. Spotlight can also perform Boolean searches. AND is implied by searching for multiple words; however, OR can be stated with the | symbol. For example, Web | Internet means search for documents that contain the word "Web" or the word "Internet."
As is customary, in order to speed up desktop searching, Mac OS X indexes all the files in the computer. See desktop search
Spotlight Category Preferences
Spotlight searches for data in all these types of files within the computer unless the user unchecks a particular category.