The protocol data unit (PDU) for the application layer in the Internet stack is
Explanation: The Protocol Data Unit is the unit of communication at a particular layer.
The Layer 1 (Physical Layer) PDU is the bit or, more generally, symbol The Layer 2 (Data Link Layer) PDU is the frame. The Layer 3 (Network Layer) PDU is the packet. The Layer 4 (Transport Layer) PDU is the segment for TCP or the datagram for UDP. The Layer 5 (Application Layer) PDU is the data or message.