Google ranking systems
Google's documented list of the systems that generate rankings, distinguished from one-off 'updates' to those systems, and…
GoogleSystemConfirmedHigh impact
RankBrain
Machine-learning system that interprets unfamiliar queries by relating them to concepts Google already understands.
What changed
RankBrain was revealed in an October 2015 interview rather than a formal announcement, and Google said it had already been running for months and was among the top three ranking signals. Its role is to map never-before-seen queries, then roughly 15% of daily searches, onto known concepts so that relevant documents can be retrieved. Google has consistently said there is nothing to optimise for RankBrain specifically. It remains listed among Google's ranking systems.
Timing
Rollout began 26 October 2015. No completion date was announced. Rankings typically remain unstable for the whole rollout window, so measurements taken inside it are not a reliable read on the outcome.
What it affected
Related terminology
RankBrain
Google's first machine-learning ranking system, introduced in 2015, which helps interpret how queries relate to concepts…
Semantic search
Retrieval based on the meaning of a query and documents rather than literal keyword matching, using entities, context and…