An expert system is a type of computer program designed to mimic the decision-making abilities of a human expert in a specific field. These systems use a set of rules and knowledge bases to analyze information and provide solutions or recommendations. They are commonly used in areas like medicine, finance, and engineering to assist professionals in making informed decisions. The core components of an expert system include a knowledge base, which contains domain-specific information, and an inference engine that applies logical rules to the knowledge base. By simulating human reasoning, expert systems can help users solve complex problems more efficiently, making them valuable tools in various industries.