What is a three-way handshake?

"So in layman's terms, I would define a three-way handshake as a way for two devices on a network to start and confirm a session. In other words, it's a three-step process used on a TCP/IP network to make a connection between the server and the client, requiring them to exchange synchronization and acknowledgment packets before the real data communication starts. First, Device A sends a TCP SYN packet comprised of random numbers to the destination server. Next, the server responds by sending an acknowledgment number and Device A's number plus 1. Finally, Device A confirms that it received both numbers by sending back the ACK plus 1, which establishes the session."