Final answer:
A UI refers to 'user interface,' which is the space where interactions between humans and machines occur. It aims to provide an intuitive and efficient experience for the user.
Step-by-step explanation:
A UI, or user interface, is the part of a software program or device that users interact with to control and use the functions of the device or program. The UI is focused on the look, feel, and usability for the human user. This can include things like buttons, text, images, sliders, and all the elements that a person interacts with on a website, app, or electronic device.
To answer your question, c. user interface is the correct definition for UI. The goal of a good UI is to make the user's experience as intuitive and efficient as possible, requiring minimal effort to achieve their desired outcome when interacting with the software or device.