Latency can be described as the delay that happens before a data transfer occurs and "high latency" is usually due to some kind of bottleneck on the network. Basically, it is the time it takes your computer to send a signal to the edge of the network and then receive a response back. Latency should not be confused with other measurements such as "data transfer rate" and "bandwidth," which refer to the speed of the data transfer itself.
At Common Networks, we report a 10 millisecond "ping" to the edge of our network, which is considered very low. What this means in regards to our service is that you should never have any problems streaming video, playing online games or video conferencing due to high latency.