I don't think they have any particular name for it. Just referred to as 'arrays from forms' or the like.
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. For example, let's post a form to itself and upon submission display the data:
(and following "Example #3" on http://us2.php.net/manual/en/language.variables.external.php)
Related FAQ is How do I create arrays in a HTML <form>?
The AnotherArray array will now contain the keys 0, 1, email and phone.
(for those lucky enough not to have PHP on the brain, PHP's "array" serves as both a perl 'array' and 'hash')