Final answer:
The first segment transferred when a TCP session begins is called SYN (Option B), part of the TCP three-way handshake for establishing a reliable connection.
Step-by-step explanation:
When a TCP session begins, the name of the first segment that is transferred is SYN (Synchronize). This is part of the TCP three-way handshake process, which initiates a reliable connection between the client and the server. The three steps of this handshake include the client sending a SYN packet to the server, the server responding with a SYN-ACK packet, and the client then sending an ACK packet to acknowledge the response, thereby establishing a connection.