A radio button is an element usually found in forms and its main purpose is to allow the user to select a single option from a group of options.

Unlike check boxes where a user is allowed to select multiple boxes, a user may only choose a single option for a radio button which makes it ideal for options like gender and civil status since a person may only have one of those.

Since the choices employing a radio button are mutually exclusive, when the user selects one, the previous selected radio button in the same group is deselected and the new one becomes the selection.

Radio buttons are so named because of their similarity to the circular buttons in old electronic devices, and specifically old car radios where there were multiple physical buttons, but the user could only press one at a time.