The three-way handshake is a TCP/IP process for establishing a reliable connection between a client and a server, involving three steps: a client sends a SYN (synchronize) packet with a random initial sequence number to the server; the server responds with a SYN-ACK (synchronize-acknowledge) packet containing its own sequence number and acknowledging the client's SYN; and finally, the client sends an ACK (acknowledge) packet to confirm receipt of the SYN-ACK, at which point the connection is established for data transfer.