The duckhead is the section of the adapter that can be removed and replaced by a different one from the Travel Kit.
This is a U.S. duckhead:

This is a EU duckhead:

All the different connectors in the Travel adapter kit are duckheads. The travel kit only includes duckheads.

Depending on the type of charger you have for your iPhone, you may or may not be able to use the Travel Adapter kit with it.
The travel kit can be used with the square 2 piece charger:


It cannot be used with the USB-C one piece chargers.
