Google's New Guide to Ranking Systems

Google has just released a new guide which will keep individuals informed about which ranking systems are in use and which ones have been retired. Google has included new terminology in its most recent guide, making a distinction between ranking "systems" and ranking "updates." A system, for example RankBrain, is always running in the background. On the other hand, an update refers to a onetime change to ranking systems. An AI system that helps Google to match queries with concept representations on pages, as well as surface local news sources when relevant. Google employs multiple systems in order to show reliable information, such as elevating authoritative pages, demoting low-quality content, and rewarding quality journalism. This AI system also helps Google to ensure that original content is shown prominently in search results, ahead of content that merely cites it. The following systems were noteable in the past, but have either been integrated into other systems or are no longer used by Google. This includes a mobile-friendly ranking system, the Penguin system which demoted websites with spammy linkbuilding practices, and the Panda system which preferred high-quality and original content.

(source: https://www.searchenginejournal.com/google-publishes-guide-to-current-retired-ranking-systems/471940/)