An Expert System is a computer-based application that mimics human expertise to solve complex problems within a specific domain. It uses a knowledge base, containing facts and heuristics, and an inference engine that applies logical rules to analyze and interpret data. Expert systems are designed to assist decision-making by providing recommendations, diagnoses, or solutions, often used in fields like medicine, engineering, and business. They rely on techniques such as rule-based reasoning and machine learning to simulate human intelligence, improving efficiency and accuracy in specialized tasks.