What does the "Past Due" warning indicate in order history

The "Past Due" label is referring to payment and is triggered by one of the following 

• The payment terms set up in the customer profile (this does not backdate existing invoices) 
  • If the terms are setup and the invoice is not yet overdue for payment, the notice will not show
• The paid status of the invoice 
  • Once marked as paid, the notice will be removed
• The export status 
  • Once exported, the "past due" will be removed and the assumption is made that payment is being processed in your accounting system