A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure

We can say that index means collecting that data from your website pages and sending it to Google. This way, when we update anything on your website, we can request a search engine to crawl it.

Indexing is how search engines organize the information and the websites that they know about. Indexing is part of a normal search engine process – arguably the most important, because content that is not in the index has no possibility of ranking for a search result. Googles most recent major change, called Mobile-First Indexing, was described by Google as a change that allows the mobile bot to crawl and index content, rather than the desktop version of the bot.