latency

Time needed for an electronic message to travel across a communications system and for the remote system to respond. Latency is inherent in all computer systems because nothing happens instantly, but usually things happen so quickly that the delay does not matter. However, latency is a critical factor in real-time systems where something is being controlled: a robot arm, for example, or an aircraft wing. It particularly concerns users when they want things to happen quickly – as when playing fast action games over a network – or when distance means the latency (delay) is very large. For example, a control message could take hours or days to reach a spacecraft.