An Expert System is a computer-based system designed to simulate human expert decision-making in a specific domain. It uses a knowledge base containing facts and heuristics, along with an inference engine that applies logical rules to derive conclusions or solve complex problems. Expert systems assist in tasks such as medical diagnosis, engineering troubleshooting, and financial analysis by mimicking expert reasoning. They provide recommendations, explanations, and justifications for their decisions, making them valuable in environments where human expertise is limited or costly. Early expert systems, such as MYCIN for medical diagnosis, demonstrated the potential of artificial intelligence in specialized fields.