Custom fields are a feature of the premium version of Order Tracking that let you add extra fields to your orders, which can be used to display extra information on the tracking page as well as in the customer order form.
The custom fields are very versatile and can be used in many different ways. For example, you can create a field to add info about order quantity, estimated delivery, price, an external link (such as to a courier service), an extra date stamp, etc. The possible uses are endless.
For more info on custom fields, please see the following sections: