A Dropdown is a list in which the selected item is always visible, and the others are visible on demand by clicking a drop-down button. They are used to simplify the design and make a choice within the UI. When closed, only the selected item is visible. When users click the drop-down button, all the options become visible. To change the value, users open the list and click another value or use the arrow keys (up and down) to select a new value.