The EntityExtractor node in Haystack allows users to extract structured information from unstructured text data using transformer-based language models. It enables the creation of knowledge graphs and can be used for various applications such as creating new metadata, filtering knowledge bases, and enriching existing databases. The node is part of a larger framework that includes indexing and query pipelines, which work together to extract entities and their relationships from large textual knowledge bases. By using the EntityExtractor, users can create structured knowledge graphs that provide in-depth information about the corpus' entities and their connections, making it easier to analyze and understand complex data.