What are the different status of the orders mean?

Here is the list of the order status in RTPro:

• Empty No items are checked out
• Active Some items are checked out, nothing returned.
• PartRet Some items are returned
• Returned All items are returned
• RetBilled All items are returned and order is billed at least once.
• Billed Order is billed at least once.
• Closed All items are returned, and order is completely billed.