This article explains all of the Forms payment statuses and their meanings.
It's important to note these are merely labels; they do not take any action on the credit card or merchant account. You cannot resubmit or refund a credit card transaction by changing these statuses. That can only be done in your merchant account/gateway interface.
Online payment statuses
A payment processed successfully through a payment gateway will be indicated with a Paid status. If an online payment is not completed/valid, then the form will not submit, no submission will be recorded, and no payment status will be available.
Offline payment statuses
When a form is submitted with an offline payment option selected, the payment status is set to Unpaid. The form admin can manually change this status to Paid when payment has been received.