LlamaIndex is an open-source data framework designed to simplify the integration of private or domain-specific data with large language models. It provides a comprehensive set of tools for data ingestion, structuring, and retrieval, enabling developers to build powerful applications through Retrieval-Augmented Generation (RAG). The framework allows users to connect to diverse data sources like APIs, PDFs, and SQL databases, index the data for efficient querying, and use natural language to retrieve relevant context, thereby enhancing the LLM's knowledge and reducing hallucinations.