Catalogued for fast searching. When multiple documents are indexed as a group, such as the billions of Web pages by the search engines, all words on every page wind up as pointers to those pages in indexes. For example, if the Web page abc.html contains the word "computer," abc.html is added to the "computer" index. Common words are excluded such as "and," "the," "this," "to," "for" and "that."
A Book Index
When an individual book or document is indexed, important words and phrases are determined first and then made into a keyword list. The list is matched against all the pages, and for every match, the page number is added to the keyword item. The keywords are sorted alphabetically and become the index at the end of the book.