Entity is a distinct thing that can be identified, described, and related to other things, such as a person, business, place, or concept.
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
Two consultants share the same name. Their biographies distinguish each person through accurate employer, location, work, and official links, reducing ambiguity about which individual a page describes.