Entities are the unit search engines actually reason about

For most of SEO's history, ranking systems worked primarily off text matching. That is no longer the whole picture.

What changed

Search systems now build and reason over knowledge graphs — structured representations of entities and the relationships between them. A page is not just a bag of keywords; it is a set of claims about entities.

What this means for content

Content that clearly identifies the entities it discusses, and their relationships to other known entities, is easier for these systems to place correctly. Vague, keyword-stuffed copy is harder to resolve into anything useful.