This is computer-language. Radio buttons are these round little button which display a black dot inside when you click on them. Generally, radio buttons come in sets of multiples even though a single one is possible. Radio buttons represent exclusive alternatives. Only one can have a black dot inside at a time. If you had selected one and click on another one, the first one is deselected, i.e., the black dot disappears, and the other one is selected.
In contrast to radio buttons, check boxes (those with checkmarks in them) represent options that may apply concurrently meaning that multiple can be selected at the same time.
Hope that helps.
