Network latency is a measure of time delay. In a packet-switched computer network like the Internet Protocol Suite, it is the round-trip delay time. This delay is often caused by congestion and results in slower observed, measured, and reported Internet speeds. Tools like Ping can measure network latency.
An important metric that is derived from network latency is called Network Jitter.
Please see Wikipedia for more details on the Ping utility.
Please see Wikipedia for more details on Network Latency.