A classification of low priority network traffic, used especially the Internet.
Different kinds of traffic have different priorities. Videoconferencing and other types of real-time communication, for example, require a certain minimum guaranteed bandwidth and latency and so must be given a high priority. Electronic mail, on the other hand, can tolerate an arbitrarily long delay and is classified as a "best-effort" service.
[Scientific American, Nov. 1994, pp. 83-84].