What is RankBrain in SEO?

Rank Brain is an artificial intelligence (AI) program used to help process Google search queries. RankBrain uses artificial intelligence to embed vast amounts of written language into mathematical entities, called vectors, that the computer can understand. Source https://montfort.io

Google's using a machine learning technology called RankBrain to help deliver its search results. Google uses a machine-learning artificial intelligence system called "RankBrain" to help sort through its search results.