A drop fee (AKA drop off fee or bobtail fee) happens when the delivery trucker is required, due to time constraints, to drop off an FCL container at the warehouse to be unloaded, and pick it up after the unloading is complete.
Bobtail fees apply to drayage shipments. When a truck offloads a full container load at a warehouse but leaves empty, the shipper will accrue a fee which is typically around half of the cost of the shipment.