Custom Basket Fields are not created ahead of time in the admin like the rest of the custom fields above. Instead they are created and accessed using a robust set of functions available in the template language which allow you to create, read and write to custom basket fields. You can think of custom basket fields as an alternate for browser cookies. When you have shopper specific data you need to collect instead of saving it as a cookie, you can leverage custom basket fields to easily save the data to the database and read it back on any page, as long as the shopper has a active session.
Examples: