Copilot Chat is an AI-powered conversational tool designed to assist developers in generating code using a test-driven development approach. It allows users to specify test cases that represent their coding intentions. Copilot Chat interacts with a large language model (LLM) to create, validate, and iteratively refine the code until it passes all test cases. This tool aims to simplify the coding process, reduce debugging time, and improve code quality by ensuring that generated code meets predefined test criteria.