Answer:
Segment.
Step-by-step explanation:
In Computer Networking, encapsulation can be defined as the process of adding a header to a data unit received by a lower layer protocol from a higher layer protocol during data transmission. This ultimately implies that, the header (segment) of a higher layer protocol such as an application layer, is the data of a lower layer such as a transportation layer in the Transmission Control Protocol and Internet Protocol (TCP/IP).
The TCP/IP model comprises of four (4) layers;
1. Application layer: this is the fourth layer of the TCP/IP model. Here, the data unit is encapsulated into segments and sent to the transport layer.
2. Transport layer (layer 3): it receives the segment and encapsulates it into packets and sends to the internet layer.
3. Internet layer (layer 2): packets are encapsulated into frames.
4. Network layer (layer 1): frames are then converted into bits and sent across the network (LAN).
Hence, the data unit encapsulated inside a packet is known as segment, which is typically referred to as packet segmentation.
Additionally, these data, segments, packets, frames and bits transmitted across various layers are known as protocol data units (PDUs).