What defines a 'user interface'?

A user interface defines the method by which a user interacts with a computer. This encompasses all the interactions a user has with the system, including how commands are input, the responses the system provides, and the overall experience of navigating through applications. A user interface can take many forms, such as graphical user interfaces (GUIs) that include visual elements like buttons and icons, or command-line interfaces (CLIs) that rely on text commands.

Understanding this definition is crucial because it highlights that a user interface is fundamentally about interaction, not just the tools or hardware involved. This perspective helps in grasping the broader scope of user experience design, which aims to make these interactions as intuitive and efficient as possible.