The significance of user interface design lies in its impact on user experience and usability of applications or websites. A well-designed user interface ensures that interactions are intuitive, efficient, and engaging, which enhances user satisfaction. By prioritizing factors such as layout, color schemes, and navigation, UI design facilitates seamless user interactions and minimizes confusion. Effective user interface design not only improves functionality but also boosts user retention and brand loyalty, making it crucial for the success of digital products.