The index of a search system is the database stored in a search server based on which search of information required by a user is executed. As a rule, it contains links to indexed resources and compressed copies of webpages.
The copy of a page in the index is the inverted file where for every word available in a source document the positions where it is found are enumerated. At the same time negative keywords are discarded, the words can be reduced to original form.
The index is being replenished by a search engine robot during periodic Internet crawls.