Named entity
A named entity is an identifiable real-world object — person, organization, place, or product — that machines distinguish from a plain string of characters. Modern engines index entities as much as they index keywords.
In practice
Entity work means resolving ambiguity: a stable name, recurring definition, consistent attributes (headquarters, founding date, leadership), and markup that ties it all together. A brand with a generic name pays this handicap every time it is mentioned. A well-defined entity gets correctly attributed in generated responses.