Latency is a modern term in computers networking and it is used to describe the time it takes data to travel from one node to another. There is another consideration. When there is a transmisión of data and return back to the source, the total time for the round trip is also considered as latency.
There are other elements to be considered when we refer to this term.
In network transmission, the following four elements are involved in latency: Delay in Storage, Device Processing, Transmission and Propagation
But when we are referring to digital information communication, scientist measure one-way latency by counting the total time it takes data to travel from its original source of information to its final destination.