Zero Latency involves a situation or state where no time is lost in exchange of information from one interface to another. It’s the immediate exchange of information across the system in real time.
Response time always has two parts: the time taken for the server to receive information, compute the response, and send out the response, and the time is taken for data to pass through the network between the client computer and the server, and back again. The latter is the network latency, also known as round trip time (RTT) latency. While there are usually ways to reduce the latencies and improve response time inside a data centre