Rule-based expert systems are a type of AI system that uses predefined rules to mimic human decision-making in specialized domains. These systems consist of a knowledge base containing if-then rules and an inference engine that applies logical reasoning to analyze data and derive conclusions. They are widely used in areas like medical diagnosis, troubleshooting, and financial analysis, where structured decision-making is essential. Rule-based systems are easy to interpret and modify but can become complex and difficult to maintain as the number of rules increases. Despite their limitations, they remain valuable for solving well-defined problems with clear logical relationships.