Indexing occurs after the results of the search engine gathering data from an algorithm and places it into its database.

Indexing refers to the process of search engines placing information into their proprietary databases, which they have retrieved from crawling the web. When a person uses a search engine to initiate an online search, the results that are displayed on the engine's SERP is drawn from the engine's database, or index. Each search engine uses its own algorithms and methodology for determining what results it will display based on the search query.