What it sounds like
Frequency grouping, Once-off, radio button, not checked, 1 of 2
This is great because the user knows the name of each control, the name of the group, and how many there are.
What it looks like
<fieldset>
<legend>Frequency</legend>
<input type="radio" id="once-off" name="repetition" value="Once-off" />
<label for="once-off">Once-off</label>
<input type="radio" id="repeating" name="repetition" value="repeating" />
<label for="repeating">Repeating</label>
</fieldset>