Delayed Acknowledgment is a technique used in TCP protocol to optimize network performance by reducing the number of packets transmitted over the network. It involves delaying the sending of acknowledgement packets for received data packets until either a certain amount of data has been received or a certain amount of time has elapsed. This technique reduces the number of acknowledgements sent and thus reduces the overall network traffic. However, excessive delay in acknowledgements can also lead to decreased network performance as it can cause unnecessary timeouts and retransmissions.