What do we call a person who interacts with a system, product or service?

The term that best describes a person who interacts with a system, product, or service is "User." In the context of user experience (UX), a user is anyone who engages with a product, whether through direct interaction or indirectly through various stages of usage. This term encompasses a broad range of individuals, including consumers, clients, and participants, but specifically highlights their role and experience while interacting with a digital product or system.

Understanding the role of the user is crucial in UX design, as it focuses on their needs, behaviors, and pain points to create more effective and user-friendly experiences. By empathizing with users, designers can ensure that the final product truly meets their expectations and enhances usability.