Latency is simply the round-trip time it takes for a packet to reach a remote point (node) and a response to get back to you, typically measured in thousandths of a second (milliseconds, or simply "ms"). When everything is working properly, the latency of consecutive measurements will be consistent and in a normal range (40 ms to 200 ms for cable modem or DSL, higher or lower for other forms or broadband). Erratic latency is a sign of trouble.