The user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is effective operation and control of the machine on the user's end, and feedback from the machine, which aids the user in making operational decisions.
Examples of user interfaces include computer keyboards and screens, control knobs in a car, and the buttons on a smartphone. In software and computer-based systems, the user interface includes elements like windows, icons, buttons, menus, and scroll bars.
A well-designed user interface should be intuitive, efficient, and provide a user-friendly experience for the user, making it easy for the user to interact with the system or software.