LangChain is an open-source Python framework that simplifies building LLM applications by providing standard interfaces for chat models, embeddings, and vector stores. It offers key components like chains for sequential operations, agents for autonomous decision-making, memory for conversation context, tools for external integrations, and vector stores for retrieval-augmented generation. The framework abstracts away complexity when connecting LLMs to external data sources and APIs, making it easier to build chatbots, question-answering systems, and other AI applications without reinventing common functionality.