RankBrain is an AI system Google uses to help understand how words relate to concepts, so it can interpret searches beyond exact keyword matches. This helps Google return relevant pages even when the content does not contain all the same words the searcher used, because the system can recognize related meanings and topics.
What that means for SEO is that clear writing and accurate, complete answers matter more than repeating an exact phrase. If your page explains a topic in a straightforward way, uses precise terms, and supports the main idea with relevant details, it is easier for Google to connect your content to the intent behind a query. RankBrain is also used to help rank results, so reducing ambiguity with descriptive headings, consistent terminology, and well organized sections can improve how confidently your page is understood and evaluated.