Brand Mentions is references to a brand online, with or without a hyperlink.
It matters because search behavior is becoming more conversational and answer-driven. Clear, authoritative, well-structured content gives both users and AI systems a better chance of understanding and referencing your brand accurately.
Example
A local newspaper names a business in an event report without linking its website. That is a brand mention, but the business should not count it as a backlink or assume it produces a particular search-ranking change.