A knowledge graph is a structured database that organizes and connects information to provide a comprehensive understanding of a particular topic or domain. It uses semantic relationships to link entities, such as people, places, and concepts, and their attributes, creating a network of interconnected data. Knowledge graphs are used by search engines like Google to enhance search results and provide users with more relevant and contextual information. They enable the display of rich snippets, knowledge panels, and other features that enhance the user experience and improve search engine optimization (SEO) efforts.