Latency
The elapsed time from initiating a data request to the beginning of the data
transfer.
On a disk, latency is the average time for the selected sector to revolve and
be positioned under the read/write head.
In a network, latency is a delay that accumulates when a packet is momentarily
stored, analyzed, and then forwarded. High latency networks include systems,
such as satellite-based X.25 or VSAT, where the delay can be great at times.