The 'Outstanding' column for invoices will display the amount still outstanding for your customers.
For the customer row, the 'outstanding' column will display the total outstanding amount of invoices for that customer in your home currency.
The invoice row shows the outstanding amount of an invoice in the invoiced currency.
If there has been a part payment against the invoice, the outstanding amount will be underlined. This indicates that you may hover over the outstanding amount with your cursor to see the total invoiced amount.
All currencies for customer rows are exchanged using the current rate from openexchangerates.org.