When a package is tendered, a notification containing an offer to carry the shipment is sent to a service provider. This occurs when FedEx transfers the package to the USPS but before it is "out for delivery." Whenever you see "Tendered for Delivery" in your tracking details, it signifies your box has been transferred from FedEx, UPS, or DHL to the USPS, and they will be responsible for transferring it the rest of the way.