The Knowledge Graph is Google’s understanding of the world. As Google puts it, the Knowledge Graph is “our database of billions of facts about people, places and things.” The Knowledge Graph is Google’s encyclopaedia that it uses as part of its search algorithms that produce the content you find on the Search Engine Results Page (SERP), including Entity Boxes, Featured Snippets, People Also Ask, People Also Search For, and of course Knowledge Panels. A simplistic explanation is that The Knowledge Graph represents Google’s algorithmic understanding of the world.
If an entity is in the Knowledge Graph, it will generally have a Knowledge Panel when you search the name on Google.
A Knowledge Panel is the box you see on the right side of Google search results on desktop that provides users with a summary of the facts Google understands about a searched entity (person, company, podcast, movie, etc.).
Interestingly (and confusingly) presence in the Knowledge Graph does not necessarily mean the entity will have a Knowledge Panel when you search the name. And when you see a Knowledge Panel, the entity is not necessarily in the Knowledge Graph. The reasons for that are quite complex, and will require a longer article.
Here is an example of a Knowledge Panel for a person like “Jason Barnard“.