Hello Nikhil,
this means that the TU and the delivery expect the transport-delivery assignment to come from somewhere else. For example the TU is created locally and the inbound delivery expects a message from ERP or TM.
See IMG activity EWM -> Goods Receipt Process -> Inbound Delivery -> Integration with Transportation -> Define Transportation Planning Type
There is a similar IMG activity for the outbound process.
You will also find documentation at help.sap.com/ewm
Regards,
Katrin