A three way handshake is a type of network communication protocol used to establish and maintain a connection between two separate devices. It involves the exchange of information in three steps in order for both sides to confirm that they are connected. The first step is the client sending out a SYN (synchronize) packet, which asks if it can connect to the server. The second step is when the server replies with an ACK (acknowledge) packet, confirming its ability to accept connections from clients. Finally, the client responds with another ACK packet, completing the three-way handshake and preparing for data transfer between them. This process ensures that only legitimate traffic will be allowed on each side's networks by verifying each other's identity before allowing any further communication or data transmission to take place.