A knowledge graph is a knowledge base that uses a graph-structured data model or topology to integrate knowledge and data. Knowledge graphs are often used to store interlinked descriptions of entities — real-world objects, events, situations or abstract concepts — with free-form semantics,[1] not fitting into a single traditional ontology.[2]

Since the development of the Semantic Web, knowledge graphs are often associated with linked open data projects, focusing on the connections between concepts and entities.[3] The are also prominently associated with and used by search engines such as Google, Bing, and Yahoo; knowledge-engines and question-answering services such as WolframAlpha, Apple’s Siri, and Amazon Alexa; and social networks such as LinkedIn and Facebook.

https://en.wikipedia.org/wiki/Knowledge_graph