A knowledge-based agent in Artificial Intelligence (AI) is a system that uses a structured knowledge base to make decisions, solve problems, and interact with its environment intelligently. It consists of a knowledge base, which stores facts and rules, and an inference engine that applies logical reasoning to derive conclusions. These agents can learn from past experiences, update their knowledge, and make informed decisions. They are widely used in expert systems, medical diagnosis, robotics, and automated decision-making. By combining symbolic reasoning with machine learning, knowledge-based agents enhance AI's ability to handle complex tasks requiring logic, inference, and domain expertise.