User interface (UI) refers to the space where interactions between humans and machines occur. It includes everything a user sees and interacts with on a device, such as buttons, icons, and menus. A well-designed UI makes it easy for users to navigate and accomplish their tasks efficiently, enhancing their overall experience with the product. Good UI design focuses on clarity and simplicity, ensuring that users can intuitively understand how to use the application or website. This involves considering elements like color, layout, and typography. Ultimately, a strong UI helps users feel comfortable and confident while using technology, whether it's a smartphone, computer, or tablet.