Many people are familiar with the common index found at the back of a book.
It is a list of names, subjects, or terms which are covered in the book. With an index, one can quickly search for and find specific information. Without an index, a search in just one book may be long and haphazard. A search in a stack of books may be like looking for a needle in a haystack. A search on the World Wide Web may be like looking for a needle in an entire field of hay.