Indexing refers to the process by which search engines, like Google, Bing, or Yahoo, collect, parse, and store web pages in a database for the purpose of quickly and accurately responding to search queries. When a web page is indexed, it means that the search engine has visited the page, analyzed its content and structure, and added it to its index. This index is essentially a giant catalog or library of web pages from which the search engine can retrieve information when a user enters a search query.

The indexing process is critical for SEO because it determines whether or not a web page will appear in search results. If a page is not indexed, it will not be displayed in search results, no matter how relevant it might be to a query. Therefore, website owners and SEO professionals work to ensure that their site’s pages are accessible, crawlable, and structured in a way that facilitates indexing by search engines. This can involve optimizing site architecture, improving page loading speed, ensuring mobile responsiveness, and providing high-quality, relevant content, among other strategies.