Il Tag <legend> HTML

<form action="/action_page.php">
  <fieldset>
    <legend>Dati Personali:</legend>
    <label for="nome">Nome:</label>
    <input type="text" id="nome" name="nome" /><br /><br />
    <label for="cognome">Cognome:</label>
    <input type="text" id="cognome" name="cognome" /><br /><br />
    <label for="email">Email:</label>
    <input type="email" id="email" name="email" /><br /><br />
    <label for="compleanno">Compleanno:</label>
    <input type="date" id="compleanno" name="compleanno" /><br /><br />
    <input type="submit" value="Invia" />
  </fieldset>
</form>