RankBrain is an algorithm learning artificial intelligence system, the use of which by Google was confirmed on 26 October 2015. It helps Google to process search results and provide more relevant search results for users. In a 2015 interview, Google commented that RankBrain was the third most important factor in the ranking algorithm along with links and content.
If RankBrain sees a word or phrase it isn’t familiar with, the machine can make a guess as to what words or phrases might have a similar meaning and filter the result accordingly, making it more effective at handling never-before-seen search queries or keywords. Search queries are sorted into word vectors, also known as “distributed representations,” which are close to each other in terms of linguistic similarity. RankBrain attempts to map this query into words (entities) or clusters of words that have the best chance of matching it. Therefore, RankBrain attempts to guess what people mean and records the results, which adapts the results to provide better user satisfaction.
There are over 200 different ranking factors which make up the ranking algorithm, whose exact functions in the Google algorithm are not fully disclosed. When offline, RankBrain is given batches of past searches and learns by matching search results. Once RankBrain's results are verified by Google's team the system is updated and goes live again.
Google has stated that it uses Tensor processing unit ASICs for processing RankBrain requests.