In order to fully understand SEO, we need to understand the thing we’re trying to optimize, the Search Engine (aka Google, Bing, Duck, Duck Go, etc.). The Search Engine Index. Subsequent activity then feeds this information into future learnings which can affect search engine rankings going forward. Whenever someone makes a search query, all relevant pages are identified in the Search Engine Index and the algorithm creates a hierarchically ranking, the Search Engine Relevant Page (SERP) Listing, of the relevant pages and serves it up to the searcher. telling search engines not to index the page (no index tag) or to search another similar page (canonical tag).