User interface, often abbreviated as UI, refers to the visual and interactive elements of a software application, website, or other digital product that enable users to interact with it. The user interface can be thought of as the intermediary layer between the user and the underlying system, allowing users to input commands or data and receive feedback from the system.

A user interface typically includes a variety of elements, such as buttons, menus, text boxes, icons, and other graphical elements, that enable users to navigate through the application, perform actions, and interact with data. The goal of a user interface is to make it as easy and intuitive as possible for users to accomplish their tasks, whether that involves creating a document, managing a project, or interacting with other users.

Good user interface design involves a careful consideration of the needs and abilities of the target audience, as well as the goals and capabilities of the underlying system. Effective user interfaces should be easy to use, visually appealing, and responsive to user input. They should also provide clear feedback to users, making it easy to understand the results of their actions and to correct mistakes if necessary.