Defines the duration in milliseconds that the receiver waits for before it sends an acknowledgement back without waiting for any data payload. Default value = 33.
Network clients that send data to a server may do so using many different quality of service (QOS) modes, some of which (reliable modes) expect the server to send back acknowledgement of receipt of data sent.
Servers must periodically acknowledge data packets received over channels with reliable QOS modes by sending packets containing acknowledgement data (also known as "acks") back to the client. If the server were to send an acknowledgement immediately after receiving each packet from the client there would be significant overhead (the acknowledgement is a 32 or 64 bit integer, which is very small compared to the whole size of the packet which also contains the IP and the UDP header). AckDelay allows the server some time to accumulate a list of received reliable data packets to acknowledge, and decreases traffic overhead by combining many acknowledgements into a single packet.