Отправить в <form> содержание тега <option>

<form action="#" method="post">
  <input name="sectionname" id="sectionname" type="hidden" />
  <select name="URL" onchange="writeSectionName(this)">
    ...
  </select>
  <input type="submit" name="submit" value="Send 2 site" />
</form>
<script>
  function writeSectionName(select) {
    document.getElementById("sectionname").value = 
      select.options[select.selectedIndex].textContent;
  }
  window.addEventListener("load", function(){
    writeSectionName(document.querySelector("select[name='URL']"));
  });
</script>
...    
$section = $_POST['sectionname'];