The interface that describes the way users interact with computer programs and operating systems is known as a User Interface (UI). UIs can be graphical (GUI) or command-line (CLI), facilitating user interactions through visual elements like buttons, icons, and menus or text-based commands. A well-designed UI enhances user experience, promoting usability and accessibility. Effective UI design is crucial in software development, ensuring that applications are intuitive, user-friendly, and meet the needs of their target audience.