PHP also understands arrays in the context of form variables (see the related faq). You may, for example, group related variables together, or use this feature to retrieve values from a multiple select input: 

Example 3.2. More complex form variables
<form action="array.php" method="post">
   Name: <input type="text" name="personal[name]"><br>
   Email: <input type="text" name="personal[email]"><br>
   Beer: <br>
   <select multiple name="beer[]">
       <option value="warthog">Warthog
       <option value="guinness">Guinness
       <option value="stuttgarter">Stuttgarter Schwabenbräu
       </select>
   <input type="submit">
</form>