In graphical user interfaces (GUIs), a dropdown, also known as a dropdown menu or a drop-down list, is a control element that allows users to select a single option from a predefined list. When inactive, it displays a single choice; when activated, it expands to show all available options. Dropdowns help save screen space and organize content, making them a popular choice in forms, toolbars, and navigation menus. They are essential for enhancing user experience by simplifying the selection process and keeping interfaces uncluttered.