A radio button or option button is a graphical control element, often used in software user interface, to select only one of a predefined set of mutually exclusive options (i.e., use radio buttons when only one item in a list of several items can be selected). This control required user to select one of the options provided. When used in an HTML form, if no button in a group is checked, then no name-value pair is passed when the form is submitted. This control element got it's name after the physical buttons used on car radios to select preset stations. When one of the buttons was pressed, other buttons would pop out, leaving the pressed button the only button in the “pushed in” position.