What is 'value' type of the field? Could you please explain how it works:

$form['support']['priority']['#type'] = 'value';


On my site this code is used to hide Priority field. But I don't understand the logic (I'm pretty new in Drupal). What is really this 'value'.
Check Form API documentation on this. It looks like someone hid field priority from output so users can't see or change it from form, but value of this field still can be used on form handlers.