A radio button is a graphical user interface element that allows users to select one option from a set of predefined choices. When a radio button is selected, any previously selected button in the same group is automatically deselected, ensuring that only one option can be chosen at a time. This feature is commonly used in forms and surveys. Radio buttons are typically displayed as small circles, and they can be found in various applications, including web forms and software interfaces. They are part of the broader category of input controls, which also includes checkboxes and dropdown menus, helping users make selections easily.