Which term refers to an improvement of an existing product or system?

The term that refers to an improvement of an existing product or system is innovation. Innovation is the process of making significant changes to existing technologies, services, or products to enhance their value or functionality. It can involve the introduction of new ideas, methods, or improvements that make something better or more efficient.

On the other hand, invention involves creating something entirely new that has not previously existed, rather than improving something that already exists. A prototype is an early model or sample of a product used to test and validate concepts and designs, while research is a systematic investigation undertaken to discover new information or reach new understandings. These concepts are related but do not specifically denote the act of improving something that is already established.