leaf site n.
[obs.] Before pervasive TCP/IP, this term was used of a machine that merely originated and read Usenet news or mail, and did not relay any third-party traffic. It was often uttered in a critical tone; when the ratio of leaf sites to backbone, rib, and other relay sites got too high, the network tended to develop bottlenecks. Compare backbone site, rib site. Now that traffic patterns depend more on the distribution of routers than of host machines this term has largely fallen out of use.