This article is from the storage FAQ part2, by Rodney D. Van Meter with numerous contributions by others.
Generally related to normal inter-host networking, but also used as a control path for some HiPPI devices. Ampex also uses NetSCSI over ethernet to control their autochangers. Also, obviously, used for connecting many servers to their clients. Standard today is 10 Mbps, 100 Mbps (fast ethernet) is becoming more common.