The multipart page is a new module that is similar to the standard WYSIWYG page, but has some nice extra possibilities.
The idea for this is coming from the Portfolio module.

This module makes it possible to create pages that include a (mini)template that will be used to build your normal content but with extra user defined fields.

The fields are filled in the backend in a generated form and only shown in the frontend. The place where they are shown is depending on the template that is linked to the page.

Multiple templates (HTML & CSS) can be managed by the system administrator.
Normal backend users that are allowed to edit pages with this pagetype can only select a template but they will not be able to add/change/delete templates.

Finally the user defined fields can also be used in the WYSIWYG part of the page.
This allows the editor to create fixed tables with content filled from the "form".

The best way to show how it works is to have a look at the demo pages on this site.

The module is explained in detail on the Help page.