The name of the field. The form name is not shown to the user but used internally in the HTML code and URLs.
Unless you know what you are doing, it is highly recommended that you prefix the form name with <code>profile_</code> to avoid name clashes with other fields. Spaces or any other special characters except dash (-) and underscore (_) are not allowed. An example name is "profile_favorite_color" or perhaps just "profile_color".