How can hidden input fields be effectively used in PHP forms to pass additional parameters to the server?

Hidden input fields can be effectively used in PHP forms to pass additional parameters to the server by including them in the form with the attribute type="hidden". This allows you to send data along with the form submission without displaying it to the user. This is useful for passing parameters like user IDs, session tokens, or any other data that you want to send to the server without the user being able to modify it.

<form method="post" action="process.php">
  <input type="hidden" name="user_id" value="<?php echo $user_id; ?>">
  <input type="hidden" name="session_token" value="<?php echo $session_token; ?>">
  <!-- other form fields -->
  <input type="submit" value="Submit">
</form>