What's Delivered means in USPS?

This status indicates the package has been delivered to the end customer. The package will have been dropped off and the tracking should note the delivery date/time.
If for any reason any package is unable to be delivered, one of the below statuses may be encountered:
Delivery Failure -This status indicates that the package was unable to be delivered for some reason (i.e.street number not found; no secure location available; no access; etc). Typically an order that fails to deliver will be returned to sender (explained below).
Return to Sender -This status indicates that USPS attempted to deliver the package to the customer but was unable to complete delivery for some reason - generally a carrier tries multiple times to deliver a package before processing a return to sender.